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: Smoking accelerates the aging process. 
Sentence2: smoking accelerates the death of cells.

Ex Output:
Smoking


Ex Input:
Sentence1: Caverns Secrets are hidden in caves. 
Sentence2: hidden caves are formed by carbonic acid in groundwater seeping through rock and dissolving limestone.

Ex Output:
are


Ex Input:
Sentence1: eating prey requires catching prey. 
Sentence2: Spiders catch insects.

Ex Output:

catching