Isn’t it odd that, when something’s funny, you might show your teeth, change your breathing, become weak and achy in some places, and maybe even cry? In other words, why do we do this bizarre thing that is laughter? Since there’s no archaeological record of laughter, it’s impossible to say exactly how and why it evolved, but scientists have some theories. Sasha Winkler digs into the reflex. Lesson by Sasha Winkler, directed by Hanna Rybak.