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: Populations Populations are subsets of a species. 
Sentence2: Gene flow occurs when individuals move into or out of a subset of a species.
Example Output: species

Example Input: Sentence1: Among families with children the average number of offspring is 1.8. 
Sentence2: information in an organism's chromosomes cause genetic traits to be passed down to that organism's children.
Example Output: children

Example Input: Sentence1: Birds eat food that they scavenge. 
Sentence2: Beaks are adapted for food that is scavenged.
Example Output:
scavenge