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: dropping an object into water causes vibrations in the water. 
Sentence2: Dropping an object into lake causes vibrations.

Ex Output:
dropping


Ex Input:
Sentence1: Mad Cow disease is a concern. 
Sentence2: pathogens can cause Mad Cow.

Ex Output:
Cow


Ex Input:
Sentence1: All hair cells require Brn3.1 for differentiation. 
Sentence2: Hair becomes specialized through differentiation.

Ex Output:

hair