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: wind is used for producing electricity. 
Sentence2: Winds are caused by pressure differences.

Ex Output:
wind


Ex Input:
Sentence1: threatening behavior by predators causes a porcupine to extend its quills. 
Sentence2: Fishers are predators that can eat porcupines.

Ex Output:
predators


Ex Input:
Sentence1: Frogs are the most durable of the amphibians. 
Sentence2: Most frogs breathe with gills as larvae and with lungs as adults.

Ex Output:

Frogs