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: Mating is generally preceded by courtship. 
Sentence2: Mating is generally similar across species.

SOLUTION: Mating

PROBLEM: Sentence1: Antigens are proteins foreign to the body. 
Sentence2: antigens are proteins.

SOLUTION: proteins

PROBLEM: Sentence1: blowing air into a whistle causes air to vibrate inside the whistle. 
Sentence2: If the persist, blow a whistle loudly into the mouthpiece.

SOLUTION:
whistle