Minecraft wiki entry for Defeating_pyramids, associated text: When attempting to open the chest, the player must take care not to step on the two tripwires in the middle of the hall. One tripwire is in the middle hall and the other is in front of the chest. It looks like mossy cobblestone, but hidden behind some vines is a dispenser filled with arrows. The dispenser will fire once when the tripwire is stepped on or broken without shears. If the player can't break it, hugging the right hand wall will cause the arrow to fly harmlessly past the player.