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Brad Thorn passed the customary post-match drug testing procedure after the Bledisloe Cup rugby test in Sydney last Saturday although it would be no surprise had the analysis revealed the consumption of "angry pills".

Thorn, who prefers to maintain a low profile on and off the field, has undergone something of a personality transformation since the latter stages of the Super 14 - and it is a mood change that irks the All Blacks lock.

Considered a consummate professional, the 33-year-old has gradually developed a bad boy exterior, one he will look to temper in the return test against the Wallabies in Auckland tomorrow.

An early indiscretion led to his downfall in Sydney last Saturday when he was sinbinned for a high tackle on Wallabies playmaker Matt Giteau.

"I'm a six foot five guy, he [Giteau] is five 10. I felt I hit him high in the chest. Look, it probably looked pretty bad but I didn't think it actually was," said Thorn.

With the highly publicised Smit incident heading his rap sheet, Thorn accepted he might now be a marked man.

"The ref [South African Craig Joubert] never looked like he wasn't going to bring out a card on me," he said of the Sydney incident, adding: "What rugby people might not know is over a 14-15 year career I've had pretty good behaviour.

"When I go out to play for the All Blacks I don't want to take a backward step.

"My job is to be clinical and be a team player and, unfortunately, sometimes it doesn't go to plan."