Just a bit of pedantry.

Trepan has two meanings.

the most common usage is to cut a disc out of something, often used in brain surgery, but also to cut a circular shaft, as in mining.

The other, more obscure, usage is to set a trap. As entrap is an anagram of trepan, I originaly thought that it was a spelling mistake!

There is an obscure Victorian song entitled "It was my cruel parents that first did me trepan". I am never too sure which meaning of the word this refers to, but I hope its the second.

Happy hunting. Dave.