Before Bugs plays the piano, the device attached to the rigged key is visible. It has disappeared when he begins playing, then reappears.
When Yosemite Sam announces his plan to get rid of every rabbit Bugs says "This calls for 'stragedy' " but closed captioning spells it as strategy.
When Sam asks Bugs to play the piano, Bugs plays 2 distinctly different sour notes each time, but he is striking the exact same key.