 Tom s chasing Jerry around Mammy the maid, when she accidentally clobbers Tom with her broom. This makes Tom think he s a mouse, including crowding into Jerry s hole and eating cheese. Neither Jerry nor Mammy are happy about Tom s amnesia. Jerry tries to hit Tom again to change him back, but seems to have lost his aim (even a piano misses). A bowling ball does catapult Tom into the ceiling and change him back, but then on the rebound, he gets hit again and changes into a mouse again. Finally, a Rube Goldberg sequence triggered by Jerry s carelessly tossed bit of cheese drops an ironing board on Tom s head. Success! Except that Mammy, who s reached the same conclusion as Jerry, happens along with a baseball bat and changes Tom back into a mouse.