TASK DEFINITION: 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.
PROBLEM: Sentence1: Viruses are usually considered to be nonliving. 
Sentence2: Viruses are usually acquired from contact with infected animals.

SOLUTION: Viruses

PROBLEM: Sentence1: a light bulb is used for seeing in the dark. 
Sentence2: light is required for seeing.

SOLUTION: seeing

PROBLEM: Sentence1: Porcupine quills can be extraordinarily painful. 
Sentence2: threatening behavior can be painful.

SOLUTION:
painful