Brown, Fredric – “Mouse” (1949)
Alien invasion – a small ship lands outside a biologist’s apartment; conveniently “[t]here was something about it, even at the most casual look, that said alien… You couldn’t put your finger on what it was.” The ship is empty aside from a recently deceased extraterrestrial mouse. The world at large puzzles over this mystery for a few days until it is pushed out of the news by the assassination of the president and then a variety of other disasters and outbreaks of war and what have you. Most of the story is the biologist talking out loud to his beloved cat in an attempt to understand what is happening. In one of those mid-century leaps of logic, he figures that the “mouse” was simply a carrier for a non-corporeal alien that is now possessing people and causing these disasters – the alien understanding, “after a few days of study, that the world is on the brink of destroying itself and needs only a push. So it could give that push.” He then realizes the alien is residing in his cat – surprise, surprise.