THE two white tigers involved in Thursday's attack on a cleaner are exhibiting symptoms of stress.
Normally relaxed and languid, they are now on constant alert, zoo officials said yesterday.
Their ears are pricked up, and they are breathing heavily.
Only Winnie and Jippie, the two female cats which carried out the attack, are showing these symptoms.
The other white tiger in the enclosure, Omar, a male, showed no interest in the cleaner, Mr Nordin Montong, 32, and stayed well away from him.
Omar is behaving normally.
The two other cats are stressed out because of the commotion that occurred during the attack, said the zoo's assistant director Biswajit Guha.
Onlookers screamed and keepers flung objects at the animals to try to distract them on Thursday.
The cats' heightened senses were thus thrown off-kilter, Mr Guha said, adding that they were probably traumatised because they had not experienced anything like it before.
It was also the first time they had come into close contact with a human being since they arrived in Singapore from Indonesia seven years ago, Mr Guha said, and their sense of smell was probably affected.
Even during feeding and cleaning, keepers stay well clear of the big cats.
When meal times roll around, a keeper lures the cats into a holding area behind the exhibit, places about 5kg of raw meat in the enclosure, then leaves it before letting the cats back in.
Mr Guha said: 'The rule is that no one is allowed to enter an enclosure in the presence of a potentially dangerous animal.
'All staff members know this.'
Over the next few days, zoo officials will try and calm the cats down by sticking to their usual routine.
This includes checks by keepers in the mornings to make sure the tigers' bodily functions are working well, raw meat feeding sessions once daily and 'enrichment classes' three times a week.
These classes involve hurling a fibreglass ball full of raw meat into the enclosure to encourage the tigers to exercise and to stimulate their brain activity.
The white tiger exhibit is currently closed, and the animals have been restricted to the den area.
If all goes well, the cats will be let out again on Monday, and the exhibit will be reopened, said Mr Guha.
He added that the tigers were not overly aggressive, and had merely shown behaviour that comes naturally to big cats.
In fact, he said, the zoo's tigers are conditioned to the presence of human beings and are likely to be less aggressive around them than their cousins in the wild.
He added: 'It is only when they feel threatened, feel their territory is intruded upon, or view an object as potential prey that they attack. Usually, they would keep away.'
[Suicidal people can be so inconsiderate, whether they throw themselves on the train tracks and disrupt thousands of commuters, or try to feed themselves to zoo animals and traumatise the animals.]