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: bacteria can cause people to become ill. 
Sentence2: bacteria can cause people to die.
bacteria

Sentence1: Energy is the fuel for chemical reactions which run the various systems of the body. 
Sentence2: running requires fuel for chemical reactions which run the various systems of the body.
body

Sentence1: the moon revolving around the Earth causes the phases of the moon. 
Sentence2: The moon rotates around the earth.

moon