An addition to the last suggestion in >>19362. If Bob was a fighter it would explain his sensitive knees >>15444 as result of a former injury.
But my complement to the idea of using a model fist from Bob as a tool is: use the whole arm up to the shoulder. Basicly a bare-knuckled model of his arm in the victory pose one can often see from boxers. Bob was a pretty big guy. You could probable be able to (slowly and painfully) impale Laura through the backdoor by using a complete model of his arm as the last mean of punishment in memory of Bob.