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: Mammalian teeth are important for digestion. 
Sentence2: bats' teeth are important for digestion.

Ex Output:
digestion


Ex Input:
Sentence1: Many corals secrete an exoskeleton that builds up to become a coral reef. 
Sentence2: Good examples are Bubble coral, Elegance coral, Frogspawn and other Euphyllia corals.

Ex Output:
coral


Ex Input:
Sentence1: Like magnet poles push away or repel each other. 
Sentence2: Magnetism can cause objects to push away each other.

Ex Output:

away