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: if an animal lives under ground then that animal will be protected from a wild fire. 
Sentence2: animals that live under ground in California will be protected from some natural disasters.
Example Output: animal

Example Input: Sentence1: Erosion of rock makes nutrients available. 
Sentence2: rain causes nutrients to be available.
Example Output: nutrients

Example Input: Sentence1: Birds eat amphibians. 
Sentence2: Birds eat predators.
Example Output:
Birds