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: an animal requires nutrients to grow and heal. 
Sentence2: Microbes can help an animal to grow and heal.

Ex Output:
grow


Ex Input:
Sentence1: Antibiotics and vaccines are being stockpiled as Britain gears up to meet the bioterrorism threat. 
Sentence2: Antibiotics and vaccines are being stockpiled against another potential threat in the environment.

Ex Output:
Antibiotics


Ex Input:
Sentence1: Humidity is moisture in the air. 
Sentence2: Lack of humidity in the air causes low amounts of rainfall.

Ex Output:

Humidity