Why are they trending? drugslive, RIP Avalanna, Andy Williams, David Cameron, Letterman

27 September 2012 - what's trending and why?

David Cameron was welcomed on to the Late Show by host David Letterman to the tune of the house band playing Rule Britannia and dry ice pumping into the studio to replicate a London fog (Reuters)

David Cameron, Letterman

David Cameron failed the American citizenship test live on The Late Show with David Letterman last night, and had a sense of humour failure. The Eton-educated Prime Minister didn't even know what Magna Carts means. Owen Jones tweets: "If only David Cameron had gone to his local comp #magnagate"

RIP Avalanna

Justin Bieber has paid tribute to a young fan on Twitter, after the six-year-old Avalanna Routh died from a rare form of cancer. Bieber met Routh in New York earlier this year after her family created the "Get Avalanna to Meet Justin Bieber" Facebook petition.

Justin Bieber tweeted: "RIP Avalanna. i love you" and "please show respect to her and her family. say a prayer for her and for them. i miss her."

Andy Williams

Legendary singer Andy Williams, known for signature song 'Moon River,' has died, aged 84. In 1992 he settled in Branson, Missouri, where he built the $13m Andy Williams Moon River Theatre. He performed there six days a week, nine months of the year, until slowed down by illness.

#drugslive, Keith Allen, MDMA

Channel Four's shock season continues with the highly anticipated Drugs Live, where people take drugs, live. Except they don't. In last night's episode, Jon Snow and doctor Christian Jessen chatted for an hour in a studio about the effects of Ecstacy, with interspersed footage of people getting high, including a vicar, a former SAS soldier, the deputy editor of the New Scientist and the novelist Lionel Shriver. Read our review here.

Danny Dyer tweets: "It's a bit serious this drugs live it's a simple science u take it u have a fucking mad night out and then u have the hump for 3 days."