Why do people keep lists of enemies?
The National Rifle Association has published an index of its opponents. What's the point of itemising your foes?
Britney Spears is on there. So, too, was Barry Manilow, the makers of Ben & Jerry's ice cream and R&B crooners Boyz II Men.
There's also George Clooney, the Kansas City Royals baseball team, Chaka Khan, Hallmark greeting cards and the American Nurses Association.
This rather disparate group might not appear, at first glance, to have much in common.
But the names of all of them are on a list drawn up by the National Rifle Association (NRA) - an influential firearms lobbying group - of those it deems to be its opponents.
According to the NRA: "All have officially endorsed anti-gun positions."
The index - titled national Organizations With Anti-Gun Policies - appeared, according to reports, to have been removed from its original page, although another version could be found elsewhere on the site.
It includes many among its 500-plus entries that are unsurprising, such as the liberal film-maker Michael Moore and The New York Times Corporation.
But others, including actor Dick Van Dyke, singer Shania Twain and the National Parent Teacher Association, are somewhat more incongruous. Also listed are Ahmet, Diva, Dweezil and Moon Zappa, offspring of the late musician Frank, as well as his widow Gail.
The list, initially drawn up in September 2012, has attracted mockery after it was spotted by supporters of gun control and circulated on social media.
But the document belongs to a long tradition of those who have felt compelled, like Father Christmas, to categorise those whom they consider to be "naughty" rather than "nice".
President Richard Nixon's staff famously drew up a roll call of his opponents which became commonly known as the "enemies list".
Anti-Communist Senator Joe McCarthy shot to national prominence after he claimed he had a piece of paper naming subversives within the US State Department.
Such tactics have been familiar in the US ever since the Chicago Crime Commission published a "public enemy" list in 1930 of Al Capone and other hoodlums. J Edgar Hoover's FBI borrowed the concept when it began posting its 10 "most wanted" fugitives list in 1950.
British authorities adopted a similar strategy in 2009 when the names of 16 people barred from entering the UK for promoting hatred - including Islamic extremists and white supremacists - was published by then-Home Secretary Jacqui Smith.
But the idea of an "enemy of the public" can be traced all the way back to the year 68AD, when the Roman Senate declared Emperor Nero a "hostis publicus".
Part of the reason such lists persist is that very often, they prove to be a highly effective rallying point.
"Creating this type of list can help to solidify a sense of group identity," says Linda Tropp, professor of psychology at the University of Massachusetts Amherst.
"When people distrust other groups, they become more vigilant and likely to attend to any potential threats against their group."
Setting out precisely who is a friend and who is a foe has often proved to be a shrewd political tactic.
During her 11-year premiership, Margaret Thatcher was said to regularly inquire whether a member of her own party was "one of us" - that is, ideologically committed to the same policy goals as she and her allies.
Barack Obama's 2012 re-election campaign made much of the fact that Osama Bin Laden - named as the US's "public enemy number one" by Bill Clinton in 1998 - had been killed under his leadership.
But equally, drawing up lists of enemies can have a galvanising effect on the other side, too.
For those who self-identify as opponents of a particular group, appearing on such a list can be a valediction.
"It's a badge of honour," says award-winning cartoonist Tony Auth, who appears on the NRA document. "If I wasn't on it I'd be appalled."
Actor Paul Newman said his inclusion on Nixon's list was his greatest achievement. Journalist Hunter S Thompson wrote of the "gross sense of injury" he felt when he realised his name was omitted.
As a result, Tropp warns that there is a danger that both sides can become more entrenched in their positions.
"It might also inhibit the potential for compromise, as it can make it harder for people to see those who hold opposing views as anything but enemies," she adds.
The strategy can backfire in other ways, too.
Nixon's so-called "enemies list" - in fact, a series of memoranda - caused major embarrassment to the administration when its existence was revealed during the Senate's investigation into the Watergate burglaries.
The document, initially kept secret, was drawn up by presidential adviser Charles "Chuck" Colson, who was later jailed as a result of his efforts to discredit Daniel Ellsberg, who appeared on the "list".
According to Stanley Kutler, author of Abuse of Power: The New Nixon Tapes, it was a perfect example of what the historian Richard J Hofstadter termed "The Paranoid Style in American Politics" - a tendency to seek out enemies and blame complicated social problems on nefarious plots by small groups.
"There's something in the American folklore - this paranoid world view," argues Kutler.
"The psychology within the Nixon administration was very much in this mould."
Such a mindset is hardly confined to the US, of course.
A cursory search on the internet reveals millions of web pages dedicated to conspiracy theories in which self-styled truth-seekers attempt to identify the ringleaders of cabals and secret societies.
To some, such a worldview might appear terrifying, but psychologists believe it can sooth the fears of those who adopt it.
"It's comforting to have enemies - to be able to point the finger at those who are responsible for our problems," says Jerrold Post of George Washington University and author of Political Paranoia: The Psycho-politics of Hatred.
"To be able to blame one's troubles on a motivated group is psychologically quite reassuring."
Opponents may sneer. But the NRA clearly realises the slogan "know your enemy" is useful in more ways than one.