If you travel enough, there is going to be a day when your cat pees in your suitcase. It's something that only happens if you have gone out of town and left your cat behind so many times that the cat becomes determined to accompany you in the most odorous way. Basically, your cat's message is: I love you so much, I'm going to let you carry my urine sample with you.
One of the down sides of living on an island is that if you're leaving for an international flight and your cat pees in your suitcase just before you need to catch the ferry, all you can do is close the suitcase and go. At the airport, I checked my bag and didn't see it again until I arrived in New York City.
It has always surprised me that cat urine cannot be found on the Periodic Table of Elements. Cat urine is powerful stuff. When allowed to ferment in a Samsonite for over 24 hours, the odor it emits can assault people with the force of tear gas.