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.

Input: Consider 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.

Output: animal


Input: Consider Input: Sentence1: Stress is the applied force, strain is the change in shape. 
Sentence2: Paper is crumbled when stress and strain is applied in order to change the shape.

Output: Stress


Input: Consider Input: Sentence1: Olfaction is the sense of smell. 
Sentence2: Most salamanders use olfaction to find a mate.


Output: Olfaction