Daffy saying "Hmm...I can get rid of the rabbit and it'll look like an accident." is Virgil Ross, with Ross's trademark use of hand and finger gestures.
Gerry Chiniquy gets the brief shot of Daffy working on the explosive xylophone and laughing evilly.
The subsequent xylophone sequence, with the famous "Endearing Young Charms" gag is Art Davis. Again, Freleng tended to give him a lot of scenes involving something extreme -- extreme anger or extreme violence, both of which are in this particular scene.