smell wrong informal
smell fishy
smell odd

What he did know was this: something about the situation smelled wrong.

If the children smelled wrong to their protector forefathers, they were killed.

But he knew one was wrong because he smelled wrong.

So far, I didn't smell anything wrong, except my shirt.

It was more that she could smell him as a male, and he smelled utterly wrong.

They smelled utterly wrong and the hair on her neck rose.

You said it yourself-anyone not from Earth would smell wrong.

But his sympathy is not real, because the poor man simply cannot smell anything wrong himself.

Humans will smell wrong; this is established as important to kzinti.

Most alarming, though, was that the people smelled wrong.