Your finger got crushed between a rock and a hard place, and there's blood beneath your fingernail. That can be excruciating, but it doesn't have to spoil your hike. Find something metal and relatively pointy, like a needle, or even a paperclip that you've unfolded. Heat the tip with a match or lighter. Be careful! The heat will transfer up the metal, so wear gloves or hold it with a split twig. Use the hot end to bear down with a twisting motion, drilling through the nail into the pocket of blood. Work gently, and stop when blood escapes through the hole. After the blood is out and the pressure is off, the pain will subside. Put a dab of antibacterial ointment on the hole and cover it with an adhesive bandage.