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: protein is used to repair cells by the human body. 
Sentence2: Meat, fish and chicken are rich sources of protein.
protein

Sentence1: Male dogs use pheromones in urine to mark their territory. 
Sentence2: Pheromones are hormones that are thought to stimulate, through smell, sexual reactions in animals.
pheromones

Sentence1: cell division often causes growth. 
Sentence2: Cancer often causes growth.

causes