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: healing requires rest. 
Sentence2: healing requires time.

Ex Output:
healing


Ex Input:
Sentence1: harming an animal species causes that animal 's population to decrease. 
Sentence2: Oil spill sare harmful to animals and the enviroment.

Ex Output:
harming


Ex Input:
Sentence1: Insulin helps cells take up glucose from the blood. 
Sentence2: Normally the pancreas produces the right amount of insulin to move the glucose into the cells.

Ex Output:

cells