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: harming an animal species causes that animal 's population to decrease. 
Sentence2: Oil spill sare harmful to animals and the enviroment.

Ex Output:
harming


Ex Input:
Sentence1: Echinoderms use pheromones to communicate with each other. 
Sentence2: Starfish use pheromones to communicate with each other.

Ex Output:

communicate