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: natural magnetism is used for pointing north by a compass. 
Sentence2: For the ordinary compass, align to the North direction.
Example Output: north

Example Input: Sentence1: an earthquake causes the ground to shake. 
Sentence2: A number of buildings in Istanbul also were damaged in the earthquake.
Example Output: earthquake

Example Input: Sentence1: Alternation of generations allows for both asexual and sexual reproduction. 
Sentence2: Alternation of generations allows for different methods of producing offspring.
Example Output:
Alternation