The DiaboloEli 13.7 has been spending quite a bit of time with a diabolo, which is a giant yoyo controlled with two sticks and a string running between the sticks.
Basically, you whip the yoyo back and forth to build its rate of spin, and then you do all kinds of crazy things with it.
For a few months, Eli used a basic model with a metal, fixed axle, and the metal would get so hot after a few minutes that it could burn your skin, believe it or not. He just got one a few days ago that has ball bearings instead of a fixed axle, which both greatly increases the RPM of the yoyo and reduces the heat it generates.
Here's him doing some ridiculous tricks with the old diabolo: