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: Some viruses live in a dormant state inside the body. 
Sentence2: a virus can live in the brain.
Example Output: viruses

Example Input: Sentence1: For instance, glucose is a sugar. 
Sentence2: insulin helps cells take up sugar from the blood.
Example Output: sugar

Example Input: Sentence1: Placental mammals give birth to relatively large and mature infants. 
Sentence2: humans give birth to relatively large and mature infants.
Example Output:
and