The Secret Weapon (1963)

This short begins with King-Size in conference with his financial minister when a coded message arrives warning of an planned invasion by cats from the Planet Feline (pronounced Fa Lean). A call for Space Mouse is dispatched, He appears in the conference room instantly. The king orders him to go to Feline, disguised as a cat, and destroy their rocket ship. Space Mouse chooses a Siamese cat disguise.. Before he leaves, though, King-Size hands him a pill telling him to swallow it if he gets into inescapable trouble. When Space Mouse wants to know what the pill will do, King Size claims all he knows is that all secret agents take along some kind of pill for emergencies.

Unfortunately the movie The Secret Weapon is not yet available on HBO Max.