When a tiny wood fragment pierces you, your first reaction is usually to simply pluck it free. Occasionally though, those pieces bury themselves way too far down to easily grab. If that surrounding tissue gets infected, it begins puffing up as fluid gathers beneath the flesh. This buildup actually creates a tight squeeze beneath the trapped debris, slowly forcing the foreign object higher. Eventually, if fortune is on your side, your own immune system naturally pops the invader entirely out!