The Cat and the Mermouse is a 1949 American one-reel animated cartoon and is the 43rd Tom and Jerry short directed by William Hanna and Joseph Barbera and produced by Fred Quimby. It was animated by Kenneth Muse, Ed Barge, Ray Patterson, Irven Spence and Al Grandmain, scored by Scott Bradley, and released on September 3, 1949.
Tom's relaxation at the beach is interrupted by Jerry who inadvertently walks over the sunbathing Tom going fishing. Jerry goes out to the pier and casts his favourite bait: cheese. Tom pulls on the line and makes Jerry reel him in. Jerry lets go of the line and Tom struggles to stay afloat, losing the string. Tom barely catches the pier, but Jerry swings the pole at him. After a few misses, Jerry whistles and then lands a direct hit. He runs to the end of the pier and pulls off the end board. Tom can't brake, and walks the plank until Jerry pulls it out, causing Tom to fall into the sea.
Tom wakes up on the sea bed, where he finds himself still alive. He starts imitating the majestic sea creatures until he spots Jerry. The cat grabs him, but Jerry pulls away revealing that he has become a mer-mouse. Jerry swims in circles until Tom's head has done a 360, and is then grabbed again. Jerry slaps Tom's face with his tail, then twists his ears into the shape of a wrench. The cat gives chase through shipwreck windows until Tom hangs back to swallow the mouse. Jerry breaks out through Tom's left eardrum. Jerry hides and disguises himself as a seahorse to join a father seahorse leading his babies, fooling the cat for only a while. Jerry then gets lassoed and captured, but Tom gets tricked into holding a fishing line and is caught. Tom escapes and chases Jerry into another shipwreck, but Jerry closes the door on him. The anchor of the ship lands on Tom. He emerges with chain rings on his ears and neck.
Jerry steals away, but cannot brake in time to avoid a swordfish. Jerry swims back the way he came, and sees Tom with a spade ready to strike. Tom misses Jerry and whacks the swordfish's bill. Tom returns it to its proper shape, but is pursued instead. Tom hides in a barrel until Jerry signals the swordfish with red circles in form of a target around the hole in the barrel. Tom is pursued again after being impaled in the rear. He ducks and narrowly missed being struck on the head as the swordfish thrusts its bill into a pole. Tom hammers down the bill on the other side of the pole so that the swordfish cannot escape. Tom returns to chase Jerry, who has woken up an octopus. Jerry hides and Tom stands vigil. As Jerry sets out, he gets poked in the back. Soon, Tom's stung on the backside. Tom attempts to run from the octopus, but is held fast by first one, then two, then three tentacles. Seeing this, Jerry is prompted to save Tom. He seizes Tom first by the paws and then, when his grip slips, the whiskers in a deadly tug-of-war against the octopus. Tom is tugged helplessly back and forth as the tussle goes first one way then the other. Tom wakes and finds that he is back on the jetty, revealing the whole thing to be a dream. Jerry rescued Tom from the water after he fell in and is applying artificial respiration in the same rhythm as in the struggle during the final moments of Tom's dream. Tom thankfully shakes Jerry's hand and then happily submits to further removal of the water from his lungs.