I said something witty about this is class the other day, and I feel compelled to write about it.
A cat will never try to be what it is not. It will not be a dog (though cats can growl). It will not seek attention unless it wants it. A cat will leave you alone until it deigns to acknowledge your presence and will suffer your attention until its had enough. A cat will not turn out to be a wolf in sheep's clothing. It is what it is.
A cat will not tell you it's off catnip when it's not. Cats don't hide their addictions or fascinations. If they catch something--a bird, a mouse, a rat--they will proudly drop it at your feet, alive or dead. They do not hoard or hide things from you.
A cat will not tell you where it has been, even if you ask. So you don't have to hear all the sordid details about what it did last night or where it went or who it was with. A cat will come in, eat something, then stretch out on the sofa for a nap.
A cat will not borrow the car, get drunk, and wreck it. It will not borrow the car to go visit its other caretaker. It won't take your car and run off to California with someone it just met yesterday.
When a cat gets sick, it doesn't whine. It will let you schlep it to the vet's office and will sleep until it recovers. It does not expect you to wait on it hand and foot.
Cats don't pretend to listen to you. They don't listen. A cat will do what it wants to do and make no pretense of caring what you think. Cats only pay attention if you pick up a spray bottle full of water and threaten to wet them if they don't cease and desist. But, the minute your back is turned, they'll do exactly what they want.
You can leave a cat alone for a week, as long as you leave it plenty of food and water and a clean litter box. It won't invite the gang in for a party because it doesn't know how to dial the phone on purpose. A cat won't run up your phone bill and will only send email accidentally.
If a cat is mad at you, it will let you know--really--in messy and obvious ways.
I'm sure I haven't covered everything. If you read this and think of something to add, leave a comment!