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: Parasites are organisms that live off a host. 
Sentence2: roundworms may be free-living or live off a host.

SOLUTION: host

PROBLEM: Sentence1: friction causes the temperature of an object to increase. 
Sentence2: When we increase the temperature of objects, they always expand.

SOLUTION: increase

PROBLEM: Sentence1: Penetration is when the sperm and egg meet and the sperm makes it way into the egg cytoplasm. 
Sentence2: fertilization requires penetration.

SOLUTION:
Penetration