He also warned the jury against testing the can of oven cleaner allegedly used by Zhernov to see how far it would spray.
Judge Tuohy said the jury should rely on the evidence they had heard, rather than carrying out their own experiments in the jury room.
People could have strong sympathy or antipathy towards dogs, but Judge Tuohy said the jury needed to put those feelings aside.
In his closing, defence lawyer Michael Bott said his client had acted in self-defence and had only sprayed the dog once - not twice as the Crown had argued.
Under the law, everyone was justified in using reasonable force in self-defence, he said.
At the time of the incident, Zhernov had been frightened and scared.
"He acted out of a genuine fear for his personal safety," Mr Bott said.
Zhernov claimed he was acting in self-defence when he sprayed the oven cleaner, which he carried in case he was attacked by dogs.
He gave evidence today that he feared for his life after he was cornered by the dog's owner, who he said was shouting and trying to hit him.
Toko's owner, Donna Peiwharangi, yesterday gave evidence that Zhernov sprayed oven cleaner into Toko's face twice while they were out walking.
She said Zhernov was wearing safety glasses at the time.
Toko had to be treated by a vet for a burn to her eye.
