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: Mollusks are invertebrates such as the common snail. 
Sentence2: snails have no backbone.

SOLUTION: snail

PROBLEM: Sentence1: friction causes the temperature of an object to increase. 
Sentence2: Friction causes the temperature of a toy to increase.

SOLUTION: causes

PROBLEM: Sentence1: operating an automobile usually requires fossil fuels. 
Sentence2: operating an automobile usually requires animal remains.

SOLUTION:
automobile