Dogs are often described as "Man's best friend", but our greatest companion, our fellow explorer and our partner in crime has been the mouse. Whether moving with prehistoric farmers or stowing away as vessels through the ages battled unknown seas; the mouse has been a steadfast, though secretive, traveller. Recent genetic research from the mice of Madeira has shown that these rodents probably arrived with the vikings. A remarkable finding, especially as there is no archaeological evidence for vikings on Madeira.