The Same Thing that Happens to Everything Else
Let me axe you a question. What happens when a seagull flies into a rock wall? Allow me to express my answer onomatopoetically: splark. (That's a combination of the splat of the seagull and the choked squaking noise it makes). And yet they say that every action has an equal and opposite reaction. Specifically, that means the wall goes splark a little, too.