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.

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

Output: are


Input: Consider Input: Sentence1: a light bulb is used for seeing in the dark. 
Sentence2: light is required for seeing.

Output: seeing


Input: Consider Input: Sentence1: Animals lack chloroplasts. 
Sentence2: animals lack the green pigment chlorophyll.


Output: Animals