Three Is a Crowd(1950)

Little Roquefort is taking a bath while he sings about his sweetheart. Percy shows up and is curious about the picture that Roquefort has. After ridiculing him, his "evil conscience" tells him what's going to happen if the mouse and his girlfriend get hitched and have children. Percy tries to keep Roquefort's lady love away, but in the end, he loses... in more ways than one!