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: Endospores are commonly found in soil and water. 
Sentence2: Dirt is really misplaced soil.
Example Output: soil

Example Input: Sentence1: Mammals that are viviparous are called therian mammals. 
Sentence2: Mouse-sized viviparous mammals evolved by Jurassic times.
Example Output: Mammals

Example Input: Sentence1: exercise increases a body 's strength. 
Sentence2: Exercise is important to keeping strong and healthy.
Example Output:
exercise