Babies sure do love their feet. I think they enjoy putting them in their mouths just to taunt the rest of us, to remind us of what we can no longer do.
My wife started doing “baby yoga” with our boy early on – primarily a move called “toes to nose” (the description is all there in the title). I would do the move a couple of times then resort to making zurburts on the soles of his feet, to his squealing giggles.
The boy loves the word “feet” for some reason. My wife discovered its calming powers one morning when our son was crying and the usual repertoire wasn’t cutting it. She repeated it a number of times, going higher each time, and he started to laugh.