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: the Earth being tilted on its rotating axis causes seasons. 
Sentence2: the planet's orbit and tilt causes seasons.

Ex Output:
seasons


Ex Input:
Sentence1: Mollusks are invertebrates such as the common snail. 
Sentence2: Another common snail is the decollate snail.

Ex Output:
snail


Ex Input:
Sentence1: a wheeled vehicle requires smooth surfaces. 
Sentence2: Cars are vehicles and trucks are vehicles.

Ex Output:

vehicle