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: All life relies on a relatively narrow range of pH, or acidity. 
Sentence2: humans rely on a relatively narrow range of acidity.

Ex Output:
acidity


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: Balance is a proprioceptive function. 
Sentence2: proprioceptive functions allow one to sense and maintain body position.

Ex Output:

function