Here you can see another occasion when Dave resembled a piece of driftwood. Appearing more like a manatee than a cat, Dave thought he would nap like this because he wanted to imagine life on the open sea. Dave thinks he would like it out there, even if he was a piece of driftwood without much say in where his travels would take him. He isn't as averse to water as many other cats are, and we all know that he loves exploring.
Of course, it would be a bad idea for Dave to embark on such a journey. He is, after all, a cat. He might think he can catch fish or birds to eat while on his journey at sea, but he might be a little overconfident about that. It is for Dave's own good that he be confined to his home. Sometimes that makes life tough, but it makes for a better long-term approach to life.