Calling Dr. Porky (1940)

A dog thinks he is being chased by small pink elephants, and goes to the hospital. While Porky is working on medication, the pink elephants find him and cause havoc. Porky finally gives him some medication, that only works temporarily, but then sees them again. He rushes back in and is once again ill.

Unfortunately the movie Calling Dr. Porky is not yet available on HBO Max.