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 soil nutrients are cations. 
Sentence2: decomposition increases the amount of cations in the soil.
Example Output: cations

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: Mammals generate heat mainly by keeping their metabolic rate high. 
Sentence2: Dolphins generate heat by keeping their metabolic rate high.
Example Output:
generate