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: Most genes contain the instructions for a single protein. 
Sentence2: Most genes contain the instructions for protein destinations.
Example Output: Most

Example Input: Sentence1: Chordates have a complete digestive system and a closed circulatory system. 
Sentence2: animals with jaws have a complete digestive system and a closed circulatory system.
Example Output: circulatory

Example Input: Sentence1: a polar bear requires a cold environment. 
Sentence2: Lynx and polar bears have similar climate requirements.
Example Output:
bear