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: Mammalian teeth are important for digestion. 
Sentence2: bats' teeth are important for digestion.
digestion

Sentence1: the uterus is used in reproduction. 
Sentence2: Reproduction uses the same organ as menstruation.
reproduction

Sentence1: Fire has intense heat. 
Sentence2: Fire can be used to identify that liquid's boiling point.

Fire