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: Mollusks are invertebrates such as the common snail. 
Sentence2: Another common snail is the decollate snail.
Example Output: snail

Example Input: Sentence1: An astronaut is a scientist who is a space explorer. 
Sentence2: Space explorers require preserved food for long flights.
Example Output: explorer

Example Input: Sentence1: sinkholes are formed by precipitation. 
Sentence2: Sinkholes are common in the southwestern portion of the subsection.
Example Output:
sinkholes