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: Nitrogen is found in proteins, nucleic acids, and chlorophyll. 
Sentence2: Life without protein is impossible.

Output: proteins


Input: Consider Input: Sentence1: Dilation occurs when cell walls relax. 
Sentence2: Decreased oxygen levels cause blood vessels to dilate and cell walls to relax.

Output: relax


Input: Consider Input: Sentence1: Ethologists usually study how animals behave in their natural environment. 
Sentence2: Animals behave according to instinct.


Output: behave