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: conserving water can be used for survival in a dry environment. 
Sentence2: conserving water can be used for survival in deserts.
Example Output: conserving

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: The fact is that ice seldom freezes or thaws at a uniform rate. 
Sentence2: ice wedging happens at varying rates.
Example Output:
rate