An EE gave IE a pocket knife at their lunch. EE lobbed knife from his loader to IE, who was in his truck. IE reported to owner that he cut his hand when he caught the knife, which must have been opened when tossed back to him. IE went to ER and there was possible tendon damage and ER temporary closed wound. IE had surgery on 9/5/11 to reattach the tendon and repair nerve damage.