We were invovled in what will ultimately be a 5-leg relay to transport 4 kittens from Georgia to Massachusetts today. Our leg was Roanoke, VA to Westminster, MD. My fiance sat in the back seat with the kittens, who sat in their 2 carriers. We had fed them kitten chow before loading them onboard, and let them use a makeshift litter box at the FBO that we made out of a shirt box and a zip-lock back of kittie litter. They also drank an enormous amount of water at the FBO -- remember it gets really dry up there -- there's a reason pilots' lips are always chapped. The kittens slept for almost the entire flight. One insisted on watching out the window whenever he was awake, but otherwise, he slept along with the other 3 who slept almost the entire flight. (in a Diamond DA-42). I think feeding them was part of the secret, but they were completely unaffected by either the noise, or the climbs and descents. They only got a little annoyed when we hit a few bumps during climbout, but other than that, they were perfect little travellers.