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.

Ex Input:
Sentence1: folding an object causes that object to change shape. 
Sentence2: Folding an object causes that object to transform.

Ex Output:
causes


Ex Input:
Sentence1: Lymph is a fluid that leaks out of capillaries into spaces between cells. 
Sentence2: Humans are made up of trillions of cells.

Ex Output:
cells


Ex Input:
Sentence1: if a tree falls then sunlight becomes available to the surrounding plants. 
Sentence2: Plants grow better when surrounding trees fall.

Ex Output:

falls