If I was developing such a library, I'd add easter eggs into the code, tie all of them to a single, big switch and disable it by default.

Last, but not the least, I'll document it as follows:

    This code contains easter eggs which are disabled by default. If you want to enable them, set easter_eggs_enabled=true. Please note that, the eggs have their own time, and it won't make them enabled all the time.