Hmmm. Well, I'd have to say that Spike is about 97% silliness and 3% demonic entity, so it'd probably take me days to document all the zaniness that he gets up to.
Let's see ...
1) Spike's tongue occasionally loses the ability to fit inside his mouth. Consequently, he sticks it out. Sometimes, he sticks it out quite far -- about half an inch -- and then walks around like that. He does not appear to notice this.
2) Spike is unaware that his tail is attached to the rest of his body, but lives in constant paranoia that it will be stepped upon. If you come within five feet of his tail, he will yowl at you in warning. His tail has never been stepped on that I know of. Conversely, when he walks around cluttered surfaces (such as my dresser or my writing desk), his tail whacks into things and sends my belongings flying. He does not appear to notice this.
3) Spike is completely fascinated by the bathtub drain, which makes some very interesting noises when any other faucet/drain combination in the apartment is in use (the plumbing in our upstairs apartment is very closely connected). It doesn't matter where he is in our apartment -- if that drain starts making noise, he's there to investigate. But not too
closely, because there are apparently trolls living in there, who might come out and attack him. Or so I can only surmise, based on Spike's behaviour.
4) Just because something was solid glass yesterday does not mean it will still be solid glass today. It's best to keep trying (or, in other words, flinging yourself against it repeatedly) just in case.
5) Regarding hot surfaces and water, see #4. Things that were hot and/or wet yesterday may not be hot and/or wet today. You should probably stick your paws into it, just in case.
6) Despite the fact that Spike eats the exact same food for breakfast as he has for dinner, his dinner food is only acceptable if it is consumed in the bathroom instead of the kitchen. (Breakfast, however, must be served in the kitchen.) Whatever is in his bowl in the kitchen at dinnertime isn't food until it's moved into the bathroom.
7) Spike can tackle a squirrel (in our bathroom -- he's an indoor-only cat), but that big bug in the corner of our bedroom? Yeah, that's just weird. No way
he's going near that!
As for Oz ... Ozzie is a less silly cat, more of a laidback, "I just wanna sniff my 'nip and go for a nap" kind of cat. His one extremely silly behaviour is stealing my underwear (my
underwear, mind you -- not J's!) and racing around the apartment wearing it as a hat. I think that's silly enough, don't you?