Australian politicians disagree over who's to blame for actor Johnny Depp's Yorkshire terriers, Boo and Pistol, getting into the country without proper documentation. (Reuters)

Australia is threatening to kill two dogs that belong to the American movie star Johnny Depp. The two Yorkshire terriers, named Boo and Pistol, have until Saturday to leave the country, according to Australian authorities.

It's a dramatic threat, and one that has made headlines around the world. But the logic behind the threat is typical for Australia, which has some of the strictest animal quarantine laws in the world.

[Johnny Depp’s tiny dogs are in mortal danger]

According to the Australian Department of Agriculture, dogs can be imported to Australia but are required to spend at least 10 days in quarantine in the country. There are also a whole variety of other restrictions on the dogs – they can only come from an approved country, they cannot be pregnant, and they must not be a banned breed. The dogs are then required to undergo a variety of tests and be fully vaccinated and microchipped.

It's a time-consuming, expensive and complicated process, but it serves a purpose. Australia is one of a relatively small number of countries around the world that are considered rabies-free.

"The reason you can walk through a park in Brisbane and not have in the back of your mind, 'What happens if a rabid dog comes out and bites me or bites my kid,' is because we've kept that disease out," Agriculture Minister Barnaby Joyce told Australia's ABC News this week.

Johnny Depp's dogs are under fire by Australian authorities after the actor brought them into the country without quarantine. (Reuters)

The restrictions on importing dogs are just one part of a broader biosecurity policy that is notoriously strict. Australia's geographical distance from much of the rest of the world and its relatively late contact with the West means that its biological ecosystem is unlike those of many other nations. To protect this, the country restricts what can be brought into the country.

The Australian Department of Agriculture Web site has a long list explaining some of the items that must be declared or are prohibited from entry into the country. Honey, for example, must be inspected by officials, and uncooked prawns require an import permit.

Such laws have been criticized by travelers and mocked in popular media, but they do serve a point. The impact of alien species on Australian wildlife was made clear early in the 20th century, when the cane toad, indigenous to Central and South America, was introduced to north Queensland in the hope of controlling the local cane beetle population.

[This koala hugged Vladimir Putin. Now Russia wonders whether Australia killed it.]

While the toads had little impact on the beetle population, they unexpectedly thrived in their new environment. The population of a few thousand cane toads introduced in 1935 is now in the millions, according to National Geographic. The cane toads are now considered pests that the Australian government is trying to eradicate.

Despite the strict government policies, ever-increasing levels of globalization have made it extremely difficult to contain breaches like these. On Thursday the Sydney Morning Herald pointed to five recent "biosecurity disasters" that had wreaked havoc in the country. For example, the Australian government spent almost $281 million trying to wipe out fire ants, first detected in Brisbane in 2001. And there are deep fears that the rabies virus will soon spread from Indonesia.

Even considering this, some Australians do feel that killing Depp's dogs might be a step too far: Almost 10,000 people have signed an online petition asking the Agriculture Ministry not to euthanize the dogs. Depp, who brought the dogs into Australia after returning to the country on his private jet following surgery in the United States, is reportedly planning to return the dogs, according to the BBC.

The film star may well be surprised at the scandal he has caused. But he can have some solace: He isn't the only American celebrity to run afoul of Australian biosecurity laws. In 2013, a Katy Perry album that featured flower seeds in its packaging triggered an investigation from Australia's Agriculture Department.

"Most people are excited to think that there's an attachment between biosecurity and someone as popular as Katy Perry," Vanessa Findlay, Australia's chief plant protection officer, said at the time.

See also:

To much disbelief, Australia decides to knight Queen Elizabeth’s husband

Vladimir Putin’s newest enemy: Australia

Status symbols no more, abandoned golden retrievers flown from Turkey to U.S.