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.

Example Input: Sentence1: if an object is made of a material then that object has the properties of that material. 
Sentence2: If an object is made of a drug, then that object has the properties of that drug.
Example Output: made

Example Input: Sentence1: healing requires rest. 
Sentence2: Healing and cell regeneration follows.
Example Output: healing

Example Input: Sentence1: riding a bike does not cause pollution. 
Sentence2: riding a bike does not release particles.
Example Output:
bike