Yellow Carding: verb. The act of searching for and/or collecting unconventional and seemingly random objects.
Monkey Son #1 loves the library, and we are frequent patrons of it. However, somewhere along the line, Monkey Son #2 noticed that there are these mysterious yellow cards within all books brought home from the library. They are nothing more than yellow cardstock with a due date stamped on them. The strange thing is that he doesn't seem to find the cards themselves interesting, but merely likes removing them from the books and taking them to other locations. It is for this reason that our library will at times get books back from us with no cards in them, but next time has double the cards, as I've found the ones that Monkey Son #2 has moved.