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: Secondary accidents are a major problem under driving conditions of reduced visibility. 
Sentence2: Bad weather increases the risk of car accidents.
Example Output: Secondary

Example Input: Sentence1: a switch is used to start the flow of current in an electrical circuit. 
Sentence2: lights are on when there is flow of current in an electrical circuit.
Example Output: circuit

Example Input: Sentence1: smoking tobacco decreases stamina. 
Sentence2: Smoking tobacco increases the time to recover from fatigue.
Example Output:
smoking