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: triceps contracting causes a person 's elbow to straighten. 
Sentence2: muscles contracting cause a person's elbow to straighten.

Ex Output:
contracting


Ex Input:
Sentence1: Refraction is the bending of light. 
Sentence2: a rainbow is formed by bending of light by separating light into all different colors.

Ex Output:
bending


Ex Input:
Sentence1: when the body is hot , sweat is produced to cool the body. 
Sentence2: Sweat cools by evaporation.

Ex Output:

sweat