In winter, when in FL, I sew in the back bedroom with a table over the foot of the twin bed.
I opened the bobbin area to replace it and dropped the little plastic cover (as in your photo) on the floor. I saw it under the bed and reached my foot to pull it out. It was not there, so I moved everything to find it. Not there.
Had to go, hubby's dr appointment. Walking in, I felt something on the bottom of my shoe. You guessed it, it got stuck in the treads on my tennis shoes. LOL
It is now just a bit scratched. But I am glad it was not lost outside.
Jean