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: Humans have collected and grown mushrooms for food for thousands of years. 
Sentence2: Yeast and mushrooms are types of fungus.

A: mushrooms
****
Q: Sentence1: Muscles can only contract. 
Sentence2: Contraction is a type of movement.

A: contract
****
Q: Sentence1: the vanes rotating in an electric fan causes air to move. 
Sentence2: The vanes rotating in an electric fan cause gases to move.

A:
electric
****