[mesmark]

I'm American and I'd agree with Sue on this. Once you personify or personalize the animal, I'd use "who".

In Sue's example from before, if no personification were added,
Now at the zoo we can see a lion, a horse and a seal. One of them eats meat, one eats hay, and one eats fish. Which one eats fish?

I'd use "which one", neither "who" nor "what".