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: smell is used for finding food by some animals. 
Sentence2: Food includes small rodents and birds.
Example Output: food

Example Input: Sentence1: Earthquakes are natural disasters. 
Sentence2: earthquakes can cause animals to leave an environment.
Example Output: Earthquakes

Example Input: Sentence1: freezing causes a solid to form. 
Sentence2: liquid turns to solid.
Example Output:
solid