I have two cats who have to be near me at all times. One is currently snuggled next to me, the other is sitting on the arm of the couch.

One cat is definitely smarter than the other. My first cat knows my car. According to my neighbor (who is sitting on her balcony when I come home in the morning), she only comes to the screen to meow when she sees my car...smart girl. She also "talks back." She understands commands and, when she doesn't want to do something (like "get down" or "go") she meows in retort, a sharp little snotty meow. She's also one to sit on my bed, poking at me if she thinks I've slept to long. Like, "Wake up. It's time to feed me and pay attention to me."

The other cat doesn't do any of these things. Probably because she knows they're already being done, haha.