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: wiring requires an electrical conductor. 
Sentence2: Gold is an excellent conductor of electricity.
Example Output: conductor

Example Input: Sentence1: high mountains with well-rounded peaks can be formed by collision of crustal plates. 
Sentence2: high mountains with well-rounded peaks can be formed by collision of plate tectonics.
Example Output: collision

Example Input: Sentence1: Animal migration is mystery of nature. 
Sentence2: natural disasters can cause migration.
Example Output:
migration