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

Example Input: Sentence1: waxy leaves are used for storing water by some plants. 
Sentence2: waxy leaves are used for water conservation by some plants.
Example Output: leaves

Example Input: Sentence1: Body heat is trapped in the haircoat. 
Sentence2: The haircoat of an organism helps keep it warm.
Example Output:
haircoat