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: threatening behavior by predators causes a porcupine to extend its quills. 
Sentence2: Fishers are one of the few specialized predators on porcupines.

SOLUTION: predators

PROBLEM: Sentence1: An example of a cartilaginous fish is a shark. 
Sentence2: jaws make sharks excellent predators.

SOLUTION: shark

PROBLEM: Sentence1: HIV infects and destroys helper T cells. 
Sentence2: HIV infects and destroys the brains behind immune response.

SOLUTION:
HIV