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: pathogens can cause disease. 
Sentence2: pathogens affects the immune system.

SOLUTION: pathogens

PROBLEM: Sentence1: Proper digestion is vital for nutrient absorption. 
Sentence2: Digestion is important for an animal's survival.

SOLUTION: digestion

PROBLEM: Sentence1: To couple in sexual union, to be matched or mated. 
Sentence2: Most salamanders find sexual partners by their sense of smell.

SOLUTION:
sexual