Camel's nose

When people say "the camel's nose is in the tent" what they mean is that the camel wants something and it's just the first step. The saying comes from a story about a camel who asked a man if it could put its nose in his tent. The man said yes because he thought the camel only wanted to put its nose in. Then, the camel asked if it could put its head in too, and then its neck, and then its shoulders, until finally the whole camel was in the tent. So this saying is like a warning - someone might start by asking for a small thing, but then if you're not careful they might end up taking up much more space than you wanted them to.