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: Mollusks are invertebrates such as the common snail. 
Sentence2: snails have no backbone.
Example Output: snail

Example Input: Sentence1: Weather today is said to be sunny and clear. 
Sentence2: High pressure systems cause it to be sunny.
Example Output: sunny

Example Input: Sentence1: Viruses are so small that they can be seen only with an electron microscope. 
Sentence2: viruses are so small that they can be seen only with a device developed in germany.
Example Output:
Viruses