I'm also bringing my cats, two to be exact. I was thinking perhaps it'd be best if they were checked in, 'cause then their carriers would be big enough and you could make room for a little toilet.. Only, I'm also really paranoid about whether they will take good care of the cats or not, and if there'll be a proper temperature or air in the luggage area. After reading comments here, I'm also seriously considering bringing my cats on board. My husband will be with me, so we should both be able to bring one each. I'm just worried that my cat will be loud as hell because he's siamese >.<. But rather annoy people than he dies.... I have a hard time seeing how there's room for a proper carrier under the seat though :|.