Back in the Northwest days, I flew a couple of times with the late great Five cat because it was cheaper to take him on the plane than to pay for a catsitter. He only ever left the carrier when he had to at security; like a lot of cats, he felt safer in his box than he would have taken out of it when there were far too many strange people around him.
Save for a few meows when the air pressure changed, you'd have to see the carrier to know I had a cat with me, and I always tried to end up at the opposite end of the plane as anyone who said they had allergies. Alas, the people who don't follow the rules mess it up for those of us who try to do so.