redwopnuG

The opposite of Gunpowder. Instead of exploding on contact, it implodes,

A: "What are you doing?"
B: "Making redwopnuG."
A: "Making what?"
B: "redwopnuG. It's the exact opposite of gunpowder."
A: "So... It implodes instead of explode, right?"
B: "Yeah."