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: bacteria cause food to spoil. 
Sentence2: Food poisoning occurs when spoiled food is eaten.

SOLUTION: spoil

PROBLEM: Sentence1: Oxygen fatigue is a shortage of oxygen reaching the brain. 
Sentence2: Plants can reduce fatigue during the daytime.

SOLUTION: fatigue

PROBLEM: Sentence1: a mirror is used for reflecting light. 
Sentence2: a mirror is used for reflecting images.

SOLUTION:
mirror