There are reports that Knut the polar bear cub is feeling unwell as he hasn't been seen out and about much at his home at Berlin Zoo.
The baby bear had his daily trip to his outdoor enclosure cut short on Monday after he started acting strangely.
Vets found his teeth were sore and they think he might be teething - which means growing a new set of gnashers.
They say Knut, who became famous when his mum rejected him, should feel better after having a rest.
Visitors from far and wide have been coming to the zoo to catch a glimpse of Knut.
On Monday, although they were disappointed the cub didn't make a appearance, they said they understood he had to get better.
One said: "It is such a pity, but I suppose it's best for the animal. If it has to be, I have to accept that he is just not well."
After Knut's mum rejected him he became well known around the world because some animal rights campaigners said is was wrong for zoo keepers to bring him up.
They said it would have been kinder to let him die but his fans disagreed.