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: Flowers produce seeds for reproduction. 
Sentence2: flowers require dispersal for reproduction.
Flowers

Sentence1: Sperm pass out of the body through the urethra. 
Sentence2: Sperm travel from the testicles through the vas deferens to the seminal vesicles and the prostate.
Sperm

Sentence1: cold fronts cause thunderstorms as they pass by. 
Sentence2: Thunderstorms Thunderstorms give birth to tornadoes.

thunderstorms