If you have your machine in a recessed table and there is even the smallest space anywhere, usually on the right side, sometimes small parts fall in there and hide. It happens to me rather often. Sometimes items are completely hidden under the edge of the machine, which has little feet that allow a bit of clearance under it. You'd think things would fall straight down, but no, they have more fun playing hide and seek. Another thing that can happen if there are metal parts on the foot is that the magnetic pin cushion can grab it and it can hide there among its pin friends. Another thing to try is to go into the room at night and scan the area with a flashlight. Sometimes things that are hard to see in normal light will reflect and show up that way. Good luck finding the missing foot.