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: Babies that are very large or very small at birth are less likely to survive. 
Sentence2: Babies that are very large or very small at birth are less likely to live.
Example Output: Babies

Example Input: Sentence1: threatening behavior causes a fight-or-flight response in animals. 
Sentence2: threatening behavior causes a basic survival response in animals.
Example Output:
animals