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.

[EX Q]: Sentence1: cold fronts cause thunderstorms as they pass by. 
Sentence2: Cold fronts cause lightning.
[EX A]: cold

[EX Q]: Sentence1: Amphibians have permeable skin that easily absorbs substances from the environment. 
Sentence2: Some substances are harmful to the body and block biological systems.
[EX A]: substances

[EX Q]: Sentence1: Neurons transmit nerve impulses to other cells. 
Sentence2: neurons transmit electrochemicals.
[EX A]:
Neurons