Why does my dog walk around in a circle before he lays down to sleep?

LOL, two of our three dogs do that. The ones that do sometimes even scratch at the carpet for awhile first. Are they working to make it "fluffier"? I think my smallest does it to "make it cooler". Not real sure. I have a million questions as to why my dogs (and cats) do what they do! They entertain me and make me laugh everyday with their antics.

my dog does that sometimes, too. maybe they're trying to find a good spot?