The tiny baby tree frog in the video has just swallowed a gnat.
Swallowing the gnat made her poop.
That is why she is scratching her butt with her hind leg. She is actually kicking away the feces.
When she “yawns,” she is actually burping.
All toads and frogs have to burp like that after swallowing something whole because they also swallow a lot of air.