What is the origin of the idiom "slippery as an eel" and when to use it?

The idiom "slippery as an eel" refers to the fact that eels have a slimy and slippery outer coating, which makes them difficult to hold or grasp. This idiom is used to describe someone who is evasive, elusive, or hard to pin down, especially when it comes to avoiding responsibilities, giving direct answers, or escaping from difficult situations.