Smelly Gas That Cows’ Bottoms Burp Out
Puzzle 20 of Spring Cleaning Pack
Question is: Smelly Gas That Cows’ Bottoms Burp Out
and the answer is: METHANE
Word Meaning:
METHANE — (organic chemistry, uncountable) The simplest aliphatic hydrocarbon, CH₄, being a constituent of natural gas, and one of the most abundant greenhouse gases.
Definitions from Wiktionary.