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

Example Input: Sentence1: poison causes harm to living things. 
Sentence2: Rattlesnakes can inject poisonous venom.
Example Output:
poison