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: hiding can be used for avoiding predators. 
Sentence2: Camouflage is used for avoiding predators.
Example Output: avoiding

Example Input: Sentence1: Proper digestion is vital for nutrient absorption. 
Sentence2: Digestion is important for an animal's survival.
Example Output: digestion

Example Input: Sentence1: landfills have a negative impact on the environment. 
Sentence2: Life affects environment, environment affects life.
Example Output:
environment