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: a thermometer is used to measure temperature. 
Sentence2: a thermometer is used to measure heat.
Example Output: a

Example Input: Sentence1: if soil is permeable then water easily flows through that soil. 
Sentence2: if soil is permeable then h2o easily flows through the soil.
Example Output: flows

Example Input: Sentence1: Mammals include rabbits, foxes and coyotes. 
Sentence2: Foxes conserve body heat with their hair or fur.
Example Output:
foxes