Who falls into the basement?
Sylvester's owners, Sam and Violet,  go on vacation to California, forgetting to put him outside. Sylvester abruptly notices this, finding that he is locked inside an empty house devoid of food with no milk being delivered for two weeks. He finds a cupboard full of canned tuna and cat food, but discovers that he also needs a can opener. He seemingly cannot find one, until he sees a mouse named David with it.  Sylvester begs for David to give it to him, but David throws it into his hole. Sylvester frantically tries and fails to retrieve it and David saunters away. Sylvester angrily gives chase and crashes into the mouse hole.
Sylvester tries vainly to open a can of tuna by beating it against the floor and jumping on it. When this doesn't work he tries to chop it with an axe, but just as he swings, the axe blade flies off the handle and out through the mail slot. David continues to taunt Sylvester & tosses the can opener out into the open, but Sylvester ends up crashing into the wall again. Next, Sylvester tries using an unbent metal coat hanger to retrieve the can opener, however David hooks it to a live wire and Sylvester receives an electric shock causing his fur to fry off.  Sylvester then sets up to drop a piano on the can, just before David taunts him again with offers for the can opener, prompting Sylvester to release his hold on the rope and dropping on himself.  An attempt to cut a larger hole around David's hole is foiled (in similar manner to a Bugs and Daffy shotgun routine) by David cutting a hole beneath Sylvester's feet causing him to fall into the basement.
Sylvester