Ideas for fun Fey pranks and antics?

A pair of fey pranksters will be harassing a PC expedition in the wilderness. I have a few ideas of how their light hearted fun will impact the party, but I'd love to hear your ideas of practical jokes that Fey would impart on an unsuspecting party of PCs.

It isn't meant to be mean spirited or deadly, the Fey actually like the PCs and just enjoy a good chuckle. In fact, this is a bit of a competition between the pair: a friendly bout of one-upsmanship to see who is the better prankster.