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.

[Q]: Sentence1: Many birds perform elaborate courtship dances. 
Sentence2: Many birds perform dances before they mate.
[A]: Many


[Q]: Sentence1: Refraction is the bending of light. 
Sentence2: a rainbow is formed by bending of light by separating light into all different colors.
[A]: bending


[Q]: Sentence1: glass cause refraction of light. 
Sentence2: Mirrors are plate glass.
[A]:
glass