EE WAS ASSISTING ANOTHER EE CHANGING OUT A SCREEN AT OUR KILN ROCK SCREEN. AS EE WAS TRIMMING RUBBER PIECE WITH POCKET KNITE, A SLIP IN TECHNIQUE RESULTED IN A LACERATION TO THE KNUCKLE BEHIND THE RIGHT THUMB. THIS WAS CLOSED WITH THREE SUTURES, EE RETURNED TO REGULAR DUTY THE SAME DAY.