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: folding an object causes that object to change shape. 
Sentence2: Folding an object causes that object to transform.

Output: causes


Input: Consider Input: Sentence1: a mutation in the sex cells of a parent can cause a new trait to appear in the parent 's offspring. 
Sentence2: Traits are initiated by mutation and recombination.

Output: mutation


Input: Consider Input: Sentence1: if gas is heated then that gas will expand. 
Sentence2: Nitrogen gas is the most abundant gas in the atmosphere.


Output: gas