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: healing requires rest. 
Sentence2: Healing and cell regeneration follows.

SOLUTION: healing

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

SOLUTION: proteins

PROBLEM: Sentence1: Active Sonar Active sonars transmit acoustic energy and detect targets by echolocation. 
Sentence2: echolocation is used to find objects underwater.

SOLUTION:
echolocation