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: Digestion is the process of breaking down food into components the body can absorb. 
Sentence2: Saliva starts to break down the food.
Example Output: breaking

Example Input: Sentence1: Coral reefs are made up of the accumulated exoskeletons of the coral polyp. 
Sentence2: coral polyps form reefs.
Example Output: polyp

Example Input: Sentence1: Because reptiles are vertebrates, they are chordates. 
Sentence2: vertebrates have a complete digestive system and a closed circulatory system.
Example Output:
vertebrates