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: an image in a mirror is formed by reflecting light. 
Sentence2: mirrors can be seen with our eyes.

Ex Output:
mirror


Ex Input:
Sentence1: a light bulb is used for seeing in the dark. 
Sentence2: Conventional light bulbs generate light by heating a filament.

Ex Output:
bulb


Ex Input:
Sentence1: During puberty, changes in hormones and changes in thinking contribute to mood swings. 
Sentence2: adolescence is a time of puberty.

Ex Output:

puberty