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: An example of a cartilaginous fish is a shark. 
Sentence2: jaws make sharks excellent predators.
Example Output: shark

Example Input: Sentence1: After about a week the larvae leave the nodules and continue to develop into adult worms. 
Sentence2: larvae leave the nodules and continue to transform until having reproductive organs.
Example Output: larvae

Example Input: Sentence1: smoking tobacco decreases stamina. 
Sentence2: Breathing someone else's tobacco smoke can be seriously harmful to one's health.
Example Output:
smoking