"Two possibilities exist: either we are alone in the Universe or we are not. Both are equally terrifying." -- Arthur C. Clark
The gnome hefts the giant tome situated on his back and then pushes his round spectacles up his protruding nose. He rubs the tip of his nose, knowing that he should really stop studying with his face so close to the books. The skin would sometimes rub off the tip during long hours of recording and study. Specks were moving on down the road, and he produces a spyglass from a loop on his hip. Through the lens, he spots a group of adventurers. He grins from ear-to-ear and gives a hoot, almost losing his balance due to the weight of the book on his back.
"These fellows look like they have purpose! It's time to find out what they're up to!"
Bag on a Stick
Very simple gag but a great one, since it can be used multiple times over, even in the same adventure. Great for tribal natives gone restless and humanoids, but anyone can have set this up. Just what the header says, a simple bag over a stick stuck in the ground or floor.
As GM you can place the bag on a stick anywhere, in a floor crack the heroes have passed before, outdoors in a clearing or path, or at the edge of the PCs' encampment the following morning, what have you. Place anything on the stick - a coiled yellow viper angered by the bag removal, mini crossbow w/poison, transdermal hallucinatory drug dusted on the bag, yellow mold colony, an NPC ally's head, a weapon, scroll tube or satchel, what have you.
The idea is to build tension and/or stall for time/distract the party. Provided it's used properly, you'll be amazed at how paranoid players will get from this simple gag.