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: camouflage is used for protection by prey against predators. 
Sentence2: blending is used for protection.

Ex Output:
protection


Ex Input:
Sentence1: Amphibians are the first true tetrapods, or vertebrates with four limbs. 
Sentence2: Frogs are classified as amphibians.

Ex Output:
Amphibians


Ex Input:
Sentence1: a light bulb is used for seeing in the dark. 
Sentence2: Heating a filament is helpful for seeing in the dark.

Ex Output:

dark