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: melting is when solids are heated above their melting point. 
Sentence2: Ice is a solid, it's cold and it's hard.
solids

Sentence1: exercise increases a body 's strength. 
Sentence2: Isometric exercise is a sustained contraction of large muscles, such as weight lifting.

exercise