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: Male dogs use pheromones in urine to mark their territory. 
Sentence2: Pheromones are hormones that are thought to stimulate, through smell, sexual reactions in animals.

Ex Output:
pheromones


Ex Input:
Sentence1: a light bulb is used for seeing in the dark. 
Sentence2: Conventional light bulbs generate light by heating a filament.

Ex Output:
bulb


Ex Input:
Sentence1: if a tree falls then sunlight becomes available to the surrounding plants. 
Sentence2: If a tree falls, then sunlight becomes available to allow growth.

Ex Output:

available