Generate an overlapping word between the given two sentences. When you find the overlapping words, they don't have to match exactly, e.g., "survival" and "survive" are valid overlapping words. Little words like "the" or "of" don't count! You must generate significant words which are not the stop words.

Q: Sentence1: Antigens are proteins foreign to the body. 
Sentence2: antigens are proteins.

A: proteins
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Q: Sentence1: Methane gas is a produced by rotting compost, trash, and human waste. 
Sentence2: Methane gas can be produced by Slime molds.

A: Methane
****
Q: Sentence1: Fireworks that only make a loud noise are called firecrackers. 
Sentence2: firecrackers can cause animals to startle.

A:
firecrackers
****