To Pet or Not to Pet

So if you are going to pet something (or someone I suppose), does that imply the critter has fur or hair?  Can you pet a fish or a Komodo Dragon or a Naked Mole Rat?  I don't know.  When you pet something your stroking it's fur but if you were to pet a worm it would just be rubbing it's skin right?  I don't know, just thought that was kind of weird...  Rabble-B