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.

Input: Consider Input: Sentence1: Arthropods Arthropods have jointed segmented exoskeletons. 
Sentence2: Insects have jointed segmented exoskeletons.

Output: exoskeletons


Input: Consider Input: Sentence1: protein is used to repair cells by the human body. 
Sentence2: Wound healing requires protein.

Output: protein


Input: Consider Input: Sentence1: Ethologists study animal behavior. 
Sentence2: Animal behavioral studies study how animals behave in their natural environment.


Output: animal