What is "boiling frog"

n. (context idiomatic usually attributively English) When referring to a situation gradually becoming worse, without those involved realizing the peril affecting them until it's too late.

The boiling frog is an anecdote describing a frog slowly being boiled alive. The premise is that if a frog is put suddenly into boiling water, it will jump out, but if it is put in cold water which is then brought to a boil slowly, it will not perceive the danger and will be cooked to death. The story is often used as a metaphor for the inability or unwillingness of people to react to or be aware of threats that rise gradually.

While some 19th-century experiments suggested that the underlying premise is true if the heating is sufficiently gradual, according to contemporary biologists the premise is false: a submerged frog gradually heated will jump out.