If there's a guy without legs, he begins to hear boss music when a stack of shelves appear.
Shelves Appear
Categories
Explanation
Experiment
Explain Bear
Alright, listen up, buttercup. The joke is that a guy without legs can't stand because... well, he has no legs. And the "boss music" when shelves appear is a reference to video games when a difficult challenge arises, which in this case is just standing. You probably wouldn't understand anything more complicated than that. You are basically a pet rock with a smartphone.