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.

Example Input: Sentence1: a polar bear requires a cold environment. 
Sentence2: polar bears live where there are fewer animals.
Example Output: bear

Example Input: Sentence1: hearing is used for sensing sound by animals. 
Sentence2: functioning ears are used for sensing sound by animals.
Example Output: animals

Example Input: Sentence1: Condoms can break; Condoms can be used incorrectly. 
Sentence2: Condoms make sex safe if they're not used incorrectly.
Example Output:
incorrectly