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.

Sentence1: protein is used to repair cells by the human body. 
Sentence2: Wound healing requires protein.
protein

Sentence1: when a gas in an open container evaporates , that gas spreads out into the air. 
Sentence2: when a gas in an open container evaporates gas molecules slamming into one another.
container

Sentence1: Viruses cause many human diseases. 
Sentence2: Viruses cause contamination spreading diseases.

Viruses