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: a mutation in the sex cells of a parent can cause a new trait to appear in the parent 's offspring. 
Sentence2: cancer of a parent's cells can cause a new trait to appear in their offspring.

Ex Output:
appear


Ex Input:
Sentence1: friction causes an object to lose energy. 
Sentence2: Friction occurs when surfaces rub together.

Ex Output:
friction


Ex Input:
Sentence1: Nitrogen deficiency increases the stress on the plants. 
Sentence2: Bacteria prevents plant stress.

Ex Output:

stress