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: pathogens can cause disease. 
Sentence2: pathogens affects the immune system.
pathogens

Sentence1: If there is enough moisture in the clouds, rain is produced. 
Sentence2: Clouds lacking water reduces rainfall.
clouds

Sentence1: a flashlight requires a source of electricity to produce light. 
Sentence2: Electrical energy is also energy.

electricity