As in their previous cartoon, Chester, oblivious to what Spike had really gone through, is disillusioned by his cowardice ("You're yellow!"), resulting in the dogs switching roles in the end.
Sylvester is chased by Spike (in this short he is called "Alfie") and Chester into the lab of Dr. Jerkyl. The cat is subjected to Dr. Jerkyl's potion that transforms him into a giant wildcat monster that claws Spike into pieces, before reverting into Sylvester just as the tinier dog comes and notices Alfie is in fear.
When the short aired on ABC's The Bugs Bunny/Looney Tunes Comedy Hour and The Bugs Bunny and Tweety Show, the short scene of Sylvester climbing and locking himself inside a trunk in Dr. Jerkyl's bedroom was cut (possibly because the censors were afraid impressionable viewers would do the same).
On CBS, the trunk part was left in, but the scene of Alfie slapping Chester in the face, spitting at his feet, and snarling, "You're yellow!" after being pummeled by a fly that drank Dr. Jerkyl's potion was cut (possibly because it was too mean).