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: hunting requires seeing prey. 
Sentence2: hunting requires seeing an animal.
Example Output: hunting

Example Input: Sentence1: Macroevolution occurs over geologic time above the level of the species. 
Sentence2: adding new genes with special capability occurs over geologic time above the level of the species.
Example Output: above

Example Input: Sentence1: condensation causes clouds to form. 
Sentence2: Clouds do create rain.
Example Output:
clouds