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.

[EX Q]: Sentence1: harming an animal species has a negative impact on the population size of that species. 
Sentence2: the rarity of a species increases harm to population exponentially.
[EX A]: harming

[EX Q]: Sentence1: Bryophytes occupy niches in moist habitats. 
Sentence2: Animals and plants that live in the same place and share resources form a community biome niche .
[EX A]: niches

[EX Q]: Sentence1: Airplanes Air travel is the quickest way to travel and is probably best for long distances. 
Sentence2: Air travel is used for moving people across bodies of water.
[EX A]:
Air