Camel's nose

The camel's nose is a metaphor for a situation where the permitting of a small, seemingly innocuous act will open the door for larger, clearly undesirable actions.

[2] Lydia Sigourney wrote another version, a widely reprinted poem for children, in which the camel enters a shop because the workman does not forbid it at any stage.

What seems at first a plausible pretext for forcing some novel case or new principle into a topic or subdivision to which it does not naturally belong, leads to hopeless confusion.

[6]In a 1915 book of fables by Horace Scudder, the story titled The Arab and His Camel ends with the moral: "It is a wise rule to resist the beginnings of evil.

There are a number of other metaphors and expressions which refer to small changes leading to chains of events with undesirable or unexpected consequences, differing in nuances.