What are some exceptions to general statements that you find noteworthy?

For example, every material in a fluid shrinks in volume as is gets colder and solifldifies, with a few exceptions, one of them being water from 4 to freezing, and from freezing into ice. This is also why water freezes from the top instead of the bottom. This is relevant because it means lakes and oceans freeze from the top and the water below is kept from freezing by the ice, making things easier for the aquatic life below.

While this is the only example I thought of, something doesn't necessarily need to be important to be "noteworthy", it can also be amusing or unintuitive.