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: Animals behave in a variety of ways which enhance their chances of survival and reproduction. 
Sentence2: Animals learn to behave to increase chances of survival.
Example Output: behave

Example Input: Sentence1: Streams may start with runoff or water seeping out of a spring. 
Sentence2: Most water comes from precipitation.
Example Output: water

Example Input: Sentence1: Food is converted into glucose. 
Sentence2: Food is converted into the type of energy that most cells use.
Example Output:
Food