[[caption-width-right:215:Whatever it is, it's alive, ''and deadly''.]]
In this 1974 horror film, diaper rash... turns into diaper ''rage''.
The Davies baby... [[EnfantTerrible came out a]] [[FetusTerrible little odd]]. It has a nasty habit of killing when it's scared. Which is pretty much all the time.
Followed by two sequels, ''It Lives Again'' (1978) and ''It's Alive 3: Island of the Alive'' (1987), as well as a very poorly-regarded 2008 [[TheRemake remake]].
!!!'''This movie contains examples of:'''
* AllThereInTheManual: The novelization provided background to why the baby turned out so screwed up (Lenore had been using experimental fertility drugs shortly after she stopped taking birth control pills).
* DownerEnding: [[spoiler: Frank manages to find an emotional connection with the baby, but the military kills it minutes later. Not to mention his wife has been driven insane due to the whole ordeal and there's more mutant babies being born all over the country.]]
* WoobieDestroyerOfWorlds: The infant(s), whose homicidal rampage turns out to be birth trauma and separation anxiety, and who longs only to be reunited with his family.
* WhatTheHellHero: Frank and his wife give each other this exchange in regards to the infant. He wanted to kill it, while she wanted to hide it.