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: Polyps usually reproduce asexually. 
Sentence2: Polyps usually reproduce several different ways.
Polyps

Sentence1: harming an animal species has a negative impact on the population size of that species. 
Sentence2: Pesticides have a negative impact on the population size of a species.
impact

Sentence1: fanning a fire increases the oxygen near the fire. 
Sentence2: Fire is a combustion reaction.

fire