detents are smaller rubber finger like parts that sit just infront of the breach of the gun to stop a ball rolling into the barrel of the gun after it is loaded infront of the bolt.
eyes are electronic sensors which are linked up to the guns board and will not allow the gun to fire unless it detects a ball in front of the bolt. this helps to avoid the gun firing when a ball is only half way into the breach, which can cause the bolt to break the paint if this happens.