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.

Sentence1: cold fronts cause thunderstorms as they pass by. 
Sentence2: Thunderstorms create havoc.
thunderstorms

Sentence1: Sex hormones are chemical messengers that control sexual development and reproduction. 
Sentence2: Androgens are male sex hormones.
Sex

Sentence1: Light contains energy. 
Sentence2: nuclear reactions in stars causes stars to produce energy.

energy