Exhaust

Hippy 1: "Dude, you have to check out my new car. It is so eco-friendly."

Hippy 2: "What kind is it, man? Hybrid? Electric? Fuel cell?"

Hippy 1: "No way dude, it runs on old cat litter and coughed up hair balls."

HIppy 2: "That's amazing, man. But what about emissions? What comes out of the tail pipe?"