Flicked piece of paper in jail cell

When Riedenschneider (Shalhoub) was in the cell with the PI, Ed and his wife, the camera is facing him while the PI reads details of Dave's past. A piece of paper is flicked right past Shalhoub while he's looking at his fingernails. I believe you can even hear the sound of it being flicked. It seems to come from the left (opposite that of the PI). Seemed like an intentional goof.