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: Enveloped viruses make their own membranes. 
Sentence2: Some viruses make their own membranes.
make

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: The Purpose of Refrigeration The fundamental reason for having a refrigerator is to keep food cold. 
Sentence2: a refrigerator keeps food fresh.

refrigerator