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: Hydrogen bonds cause water to expand when it freezes. 
Sentence2: Water freezes into ice when cooled.

SOLUTION: freezes

PROBLEM: 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.

SOLUTION: Sperm

PROBLEM: Sentence1: Mechanical energy can be changed to electrical energy. 
Sentence2: an animal's movement can be changed to electrical energy.

SOLUTION:
changed