This is Moo Deng. You can find many photos of her biting knees.

This is the video the OP still is from, she tries for the knee, but the human is too quick! (Sorry for Reddit link, I can’t find it elsewhere and can’t figure out how to save and post the video on its own)

https://www.reddit.com/r/Awwducational/comments/z07fni/the_pygmy_hippopotamus_is_the_much_smaller/

And this is a podcast about her.

https://maximumfun.org/episodes/comfort-creatures/moo-deng-and-pygmy-hippos/

He’s just a little guy, that’s how high he reaches.