Whiskers

Cat whiskers automatically grow to the width of the cat. When faced with a small opening, the whiskers tell the cat if there's enough room to fit its whole body.

I like that. Someday I dream of being really fat. Like so fat that I can't fit through some doorways.

When that day arrives, I will grow a handlebar mustache* that is as wide as my body is fat. And I will stick my giant handlebar mustache into doorways in order to see if the rest of me will fit. Nature!

* I guess it doesn't have to be a handlebar mustache. But it just seems like the classy way to go.