Of big cats and bezoars
Oh, sure, trespassers will be eaten. But they'll just be vomited up again 20 minutes from now.
And intentionally vomited up, no less.
In case you weren't aware, it is not an accident when your cat pukes up a hairball. Instead, cats induce vomiting—usually by eating grass or houseplants. It's just a normal part of cat life. First, they ingest a lot of hair and dirt by licking themselves clean. Then, they have to get it back out again.
Even big cats, like the ones this sign warns you about, produce hairballs. That's right. Pity the zookeepers.