The Devil Bat (1940)

Bela Lugosi stars as a scientist who electrifies bats, which somehow increases their size and makes them hate his new aftershave lotion.  He manufactures the lotion for the owners of the company where he works.  Bela is angry because they are getting rich from his concoctions for health and beauty products.

Thus when the rich owners put aftershave on their neck - per Bela, they should put it on "the tender part of the neck" - the devil bat screeches, swoops down upon them, bites their necks and they die a horrible death.  Take that, rich oppressor!