The legend says that if you put a frog in water and raise the temperature really really slowly, it won’t notice and it’ll eventually be boiled alive. Luckily for frogs, that’s nonsense:
While some 19th-century experiments suggested that the underlying premise is true if the heating is sufficiently gradual, according to modern biologists the premise is false: a frog that is gradually heated will jump out.Wikipedia
Don’t get me wrong; I love having a name for the “inability or unwillingness of people to react to or be aware of sinister threats that arise gradually rather than suddenly” because that’s a mouthful.
But enough with the poor frogs already! Let’s at least find a metaphor with some truth behind it.
People have been discussing the need to replace this metaphor for decades, according to some random message board comment threads I found via Google. This commenter from 2006 suggested carbon monoxide poisoning as a replacement metaphor. Thoughts?