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: moss causes chemical weathering. 
Sentence2: Sphagnum moss mixed with peat moss.

Ex Output:
moss


Ex Input:
Sentence1: dropping an object into water causes vibrations in the water. 
Sentence2: Dropping an object into lake causes vibrations.

Ex Output:
dropping


Ex Input:
Sentence1: skin is used for breathing air by frogs. 
Sentence2: Sickness can be caused by skin breathing problems.

Ex Output:

breathing