An adorable clip from the PBS series Nature takes a look at the incredibly fluid physiology of ferrets. They examine, through slow motion footage, the instantaneous switch these furry mustelas can make from moving above ground with an arched back to burrowing down underground with their spine stretched low. This is due to the specific design of their vertebrae.
This flexibility in their spine is due to a unique set of back vertebrae. In other animals, protrusions known as processes on each segment of the spine stop it from moving too far. In ferrets, these processes are thinner, creating flexibility and movement. So their spine can stretch out when they go underground, making their body 30% longer.