Lord's went silent when Steve Smith collapsed to the ground overnight after copping a sickening blow to the neck but some spectators found their voice later in the most distasteful fashion.
And questions have been raised about the response of bowler Jofra Archer, the England quick who floored Smith.
Smith was forced off the ground after ducking into the bouncer, the impact of which floored him and sparked huge fears for his health.
Play was stopped for a lengthy period and when the Australian team doctor escorted him back to the dressing room, Smith received a standing ovation as most fans were relieved to see him back on his feet.
At stumps, the test was delicately poised. England's lead went past 100 as it reached stumps at 4/96 after bowling Australia out for 250 in reply to the hosts' first-innings 258.
Smith was cleared of concussion and returned to the crease when Peter Siddle was caught behind.
Most people at Lord's stood up and applauded the former Aussie skipper as he strode back to the middle but some small pockets booed him.
Returning on 80, Smith was later trapped LBW for 92 and some sections of the crowd again gave him some stick as he walked off the ground.
In commentary for Sky Sports Shane Warne criticised the people booing, saying in a moment like this they should have shown more class, and former Australian women's captain Lisa Sthalekar also lashed out on Twitter.
Asked about the booing after play, Australian coach Justin Langer was initially at a loss for words and simply raised both his arms up in a "what can I do?" type gesture.
"What can I say? Whatever I say — I've spoken enough about the boos, there's nothing we can do about the boos," he said.
"I think people have been showing great admiration for Steve Smith from the moment he arrived in England until now, there is also a lot of people standing and applauding him.
"So there's a few people who might have been doing that (booing), but there's nothing we can do about that."
Questions over Archer's response
While England players were quick to check on Smith's welfare, some on social media took aim at Jofra Archer for appearing to smile not long after the batsman was floored as players waited around while Smith received medical attention.
Some also questioned whether the paceman went to see if Smith was OK, with the TV broadcast leaving people with the impression Archer turned away from the scene rather quickly.
Fox Sports presenter Neroli Meadows was among those to query Archer's response, as was former Australian politician Jamie Briggs.
However, others on social media suggested Archer may have walked away in the immediate aftermath out of shock rather than any indifference to Smith.
He was seen smiling next to Jos Buttler but it is unclear what drew that response.
Of course not everyone was convinced the images of Archer and Jos Buttler smiling were actually in the direction of a prone Smith, with former Aussie quick Mitchell Starc coming to the defence of Archer and Buttler.
"They weren't smiling at the situation that's 100 per cent I can tell you that now, because no one is like that," Johnson said on BBC.
"The guy (Archer) offered me a lift in Edgbaston, he doesn't even know me that well. I was waiting outside and he gets in his car and comes past and goes 'do you want a lift?'.
"Buttler as well, I played IPL cricket with him, genuinely good people."
"This is where you say the camera never lies, I think it has on this occasion because you don't know when that photo was taken," Alec Stewart added.
"You saw the England players go and see how he was, the doctors and physio and medical team are out there looking after him and you don't know if Smith has said he's fine and it was too quick for me and that's why they're smiling.
"But I promise you, as Johnson has just said, he would not have been laughing because he'd hit him."
Hughes tragedy brought to mind
Coach Justin Langer suggested the scary incident brought back memories of Phil Hughes' tragic death in 2014 after he was hit on the neck while batting.
The area where Smith was hit looked similar to where Hughes was struck, and the way Smith fell forward onto his front was also similar to the way Hughes reacted when he copped the blow during a Sheffield Shield game.
"You never like seeing your players get hit like that, no doubt about that," Langer said. "There's obviously some pretty rough memories of a blow like that so … there was no fun in it.
"There was a lot of chat, all of a sudden the concussion rule comes in and so probably the initial bit when we make sure he's OK then we saw him in the medical room and he was a bit rattled but he wasn't too bad.
"Then you start thinking about the professional side of it — who's going to be the replacement and all that sort of stuff but then as time progressed he went through all the concussion protocols and he seemed to be coming up OK.
"He passed all that then he came back in the changeroom and he had a bit of a smile on his face. He was more worried about his arm actually — his arm was sore."
Asked if he was surprised to see Smith return to the crease when the next wicket fell, Langer said: "He was determined. All that he was worried about was that he wasn't going to be able to play his forward defence because it was hurting with his top-hand grip. That's all he was worried about."
Super Smith makes history
He may have fallen short of 100 but Smith still managed to make history with another crucial innings.
By making 92, the 30-year-old notched his seventh successive half century in Ashes tests, setting an all-time record.
After scoring twin tons at Edgbaston in the series opener, Smith equalled Australian great Mike Hussey for the most consecutive scores of 50-plus in Ashes matches with six. But he went past the West Australian when he raised his bat at Lord's.
Smith's dream run has placed the blowtorch on his teammates. He received good support from fellow century-maker Matthew Wade in the second innings at Edgbaston but without him the Aussies would have struggled even more in England.
Australia was knocked over for 250 in the first dig at Lord's and after Smith, the next top score was Usman Khawaja was 36. Only two others made it to 20.
In the first innings in Birmingham Australia was 122-8 before Smith scored 144 to rescue his side and in the second innings the tourists were in trouble at 3-75 before Travis Head (51) Smith, Wade came to the party.
Australia's over-reliance on Smith may prove to be a problem on the rare occasion when he does fail.
Archer is the real deal
Australia coach Justin Langer said Australia would try to wear test debutant Jofra Archer down by forcing him to come back for fourth and fifth spells but the fast bowler showed that tactic won't work.
The 24-year-old was at his quickest during his fourth spell, when his average speed sat upwards of 145kmh. He went past the 150kmh regularly and it was during this spell he landed scary blows on Smith's forearm and neck.
Archer really cranked things up and Smith was in agony when he received a blow to the arm as he failed to get out of the way of a short ball. The batsman dropped his piece of willow immediately and play stopped as the doctor and physio came out to assess him.
Smith batted on with a large amount of tape on his arm but later went for an x-ray to see if there was any more damage than just bruising, as initially thought.
Archer was bowling serious heat after lunch, sending down what was easily the quickest spell of the match. He had Smith and Pat Cummins hopping about as the threat of danger loomed large.
That danger became very real when Archer clocked Smith in the head and he maintained the rage right to the end of a hostile eight-over spell that had the Lord's crowd rocking as it urged him to keep challenging the speed gun.
Archer finished with 2-59 from 29 overs.
England's top order fails again
Jason Roy's place at the top of the England batting order is sure to come under further scrutiny after he failed again.
He scored just 38 runs in the first test and his second-innings two at Lord's follows on from a duck in the first dig.
Roy was caught and bowled by Pat Cummins on day four and there will be plenty of debate about whether he should slide down the order for the next test in Leeds — if he keeps his place.
Roy earned a test debut at Edgbaston on the back of his brilliant one-day form which saw him help England win the World Cup but his transition to the longest format has been a rough one.
Captain Joe Root wanted to continue batting at No4 but was convinced to push up the order to first drop for the Ashes as he's struggled to make any major contributions. He was caught behind for a first-ball duck on day four at Lord's as Cummins found himself on a hat-trick and apart from a half century in his first effort at Edgbaston he's been unable to make a big score.
His tally for the series now reads: 57, 28, 14 and 0.
Joe Denly failed to convert another start and Rory Burns was unable to go big as the Poms collapsed to 4-71, giving Australia a sniff at an unlikely victory.