A Negative List is or gets complicated and unclear. There are an estimated 5,488 mammal species, so it’s much more effective to have a shorter list of permitted species, rather than a huge list of prohibited species. Negative Lists tend to focus on one particular type of risk (e.g. invasiveness or rate of extinction), which means there can be several Negative Lists, creating confusion for owners, the public and enforcers. A negative Lists is a reactive instrument. They need to be continually updated in a slow and costly bureaucratic process as new (or hybrid) species are observed being kept as pets, as the conservation status of a species becomes critical, or as incidents occur with a species threatening human and animal health and the environment. A long negative list requires that enforcers are able to not only identify, but also assess the welfare of hundreds of specific animal species, including possible crossbreeds.