You take out your knife and manage to pry loose one jewel, a perfectly white sphere of onyx like a very large pearl. You also find that it is attached to a metal key. What you do not realize is that the key is attached to a fine wire cable which immediately jerks the key from your hand and back into the hole.
You try the other jewel but the same thing happens.
Suddenly you hear the faintest of snaps. Before you know what hit you your neck is pierced by poison darts; your vision grows dim as you see small holes in the nearby trees close shut after having sprung their trap.