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: Humans have collected and grown mushrooms for food for thousands of years. 
Sentence2: humans have collected and grown porcinis for thousands of years.
Example Output: Humans

Example Input: Sentence1: if an organism becomes too hot then that organism may die. 
Sentence2: a plant can collapse if it gets too hot.
Example Output: hot

Example Input: Sentence1: volcanic ash in the atmosphere decreases the temperature by blocking the sun. 
Sentence2: Volcanic ash in the atmosphere can cause change in climate.
Example Output:
ash