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: condensing causes a liquid to form. 
Sentence2: Air carries moisture that causes a liquid to form.
Example Output: causes

Example Input: Sentence1: For instance, in the forest, plants use sunlight and soil nutrients to grow. 
Sentence2: earthworms help plants grow.
Example Output:
grow