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: Some pelycosaurs gave rise to a group of animals called therapsids. 
Sentence2: Like most other groups of synapsids, all pelycosaurs are now extinct.
Example Output: pelycosaurs

Example Input: Sentence1: Basically, heat is energy. 
Sentence2: Head hair is especially important in preventing energy loss from the body.
Example Output: energy

Example Input: Sentence1: Ice wedging is the most important form of mechanical weathering. 
Sentence2: Cycles of freezing and thawing water cause mechanical weathering.
Example Output:
mechanical