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: the moon revolving around the Earth causes the phases of the moon. 
Sentence2: Lets start our discussion of the Moon's phases with the New Moon phase.
Example Output: phases

Example Input: Sentence1: After about a week the larvae leave the nodules and continue to develop into adult worms. 
Sentence2: larvae leave the nodules and continue to transform until having reproductive organs.
Example Output:
larvae