[Amezarak]

Ferrets are commonly used in serial passaging and gain of function research.

https://nymag.com/intelligencer/article/coronavirus-lab-esca...

> In 2011, a tall, confident Dutch scientist, Ron Fouchier, using grant money from Fauci’s group at NIH, created a mutant form of highly pathogenic avian influenza, H5N1, and passaged it ten times through ferrets in order to prove that he could “force” (his word) this potentially fatal disease to infect mammals, including humans, “via aerosols or respiratory droplets.”

https://www.salon.com/2020/11/29/covid-19-mutations-spread-m...

> Because ferrets are the animals most like humans in terms of how their immune systems respond to influenza, scientists have experimented with them to make existing viruses more deadly, a biowarfare concept known as "gain of function" research.