This is a movie based on the emote glitch that allows you to get stuck in a pose.

How to get stuck in an animation:
Drag an animation that works while sitting down (i.e. happy, cheer, stretch) into your hotbar.
Do /sit on a sit-able object like a chair.
Use that button for the emote and move forward at the same time.
You'll know when it works when you play the animation at the same time as you move forward then you are frozen in the animation.