What kind of monkey business is going on when the thief rejects cash and throws bills taken from the pocket onto the ground? Watch the video!

The backstory: a monkey in Bali, Indonesia, attacked Bob, unprovoked. It leapt onto Bob’s leg and dug though his pants pocket. Finding only a crumpled tissue, which it threw to the ground, it scampered up onto Bob’s shoulder and began rifling his shoulder bag.

That gave us an idea. We thought about what pickpockets around the world have told us: they look for “the print of the money.” That is, how the shape of a wallet or credit card shows itself through the pocket fabric, how a jacket hangs heavier on one side when there’s a fat wallet in one pocket, how a pocket bulges.

So we returned to the monkeys with five bananas. We put a banana in Bob’s pocket with cash on top. A monkey spotted “the print of the goodies” immediately and went for it, tossing the cash to the ground, digging out the banana, then sitting down a safe distance away for a gobbled feast.

We repeated this four more times in different areas, and each monkey’s behavior was the same. One almost tore Bob’s pants. Another bit through the fabric in its haste.

Bob’s pockets have hosted many thieves’ hands. As thiefhunters looking for pickpockets we use the exact same technique. We place the bait deep in a pocket—tempting, but not too obvious or easy to get. Then we stroll among thieves with antennas up, nerve-endings fine-tuned, and cameras rolling.