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: Humans have collected and grown mushrooms for food for thousands of years. 
Sentence2: Yeast and mushrooms are types of fungus.

Ex Output:
mushrooms


Ex Input:
Sentence1: Plants exhibit phototropism, or growing toward a light source. 
Sentence2: Phototropism means growing toward the energy of light.

Ex Output:
phototropism


Ex Input:
Sentence1: When inside a bacterium, the spore is called an endospore . 
Sentence2: bacterium are commonly found in soil and water.

Ex Output:

bacterium