Elastoplast
Little dude rides on his bike and ends up on the floor with an injured LEFT knee. Enters his concerned mother to see a nasty coin-sized wound on his RIGHT knee. Lo and behold, after his mother is done with him the plaster has ended up on the LEFT knee. It seems that the wound on his left knee migrated to the right knee and then back to the left knee once again. A little continuity snafu perhaps?
