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 Input:
Sentence1: Fertilization occurs naturally in the fallopian tubes. 
Sentence2: fertilization is used for reproduction.

Ex Output:
Fertilization


Ex Input:
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 Output:
harming


Ex Input:
Sentence1: Evaporation is when a liquid turns into a gas. 
Sentence2: Sweat cools the body when it turns into a gas.

Ex Output:

gas