Gotcha

noun

1. A potential problem or source of trouble.

   "Review the work thoroughly and make sure there are no gotchas."

2. An instance of publicly tricking someone or exposing them to ridicule, especially by means of an elaborate deception.
3. An instance of accomplishing a tricky idea or overcoming a difficult obstacle.

   "Now here's another few gotchas that you can do to implement it."

4. A feature of a system or a program that works in the way it is documented but is counter-intuitive and almost invites mistake or non-function.

   "Wireless was the first gotcha when installing the distro."