I have rarely observed monkeys. I was traveling in the Caribbean and saw a pet monkey on a long leash. About 8 meters of leash lay flat and straight on the dusty ground. The leash was hooked on a small stump of a weed about 2 cm high near the anchored end of the leash. The monkey wanted to proceed farther but was impeded by the snagged leash. Instead of walking back to the stump and lifting the leash over it, the monkey held the leash and very quickly raised and lowered it by perhaps 10 cm. A traveling wave moved along the leash until it reached the stump whereupon the wave released the leash from the stump.

I suppose that the monkey had seen this done by a person or another monkey. He had practiced for it worked the first time. It seemed to me that he performed the action with somewhere near minimal effort. Another possibility is that the monkey did the ‘natural thing’ when the distance between monkey and stump was only 1/2 meter, and learned gradually that longer distances still worked, but only if the motion was very quick.