Ok...mystery solved! I asked Jonah this morning if it is the same foot's sock that he always takes off and he said yes...I asked if it was hot and he said no...I asked if there was a reason and he said yes! He came downstairs and showed me how he puts his left knee on a little Hess truck and likes that foot to "slide" on the ground and he uses his "sockfree" foot on the right to push his body around the room on the truck! He has done this recently some but I think he has had the sock off more than that...hhmmm...but he doesn't put it back on...he will go all day and all night sleeping like that!