As you’ve probably guessed, the commentary track on 21 Jump Street’s disc (out now, fact fans) falls into the latter category. It helps that the movie itself is an extremely funny one, and it’s evident that its directors – Chris Miller and Phil Lord – as well as its leads – Jonah Hill and Channing Tatum – had a great time making it.

Art imitates life

21 Jump Street’s opening scene sees a teenage Morton Schmidt (Hill) walk into school with a savage blonde hairdo inspired by Eminem. Although this seems like a simple visual gag to kick the movie off, Hill suggests that he really did have his hair styled after Marshall Bruce Mathers when he was a youth. “This is what I actually looked like in highschool,” he said. Channing Tatum’s character Greg Jenko, meanwhile, peers out from beneath lank, long hair parted precisely down the middle – a look, the directors reveal, inspired by Tim Riggins’ do in Friday Night Lights. Taylor Kitsch must be so proud. These pictures, it turns out, are Jonah Hill’s genuine childhood photos, borrowed from his parents. At the 21 Jump Street premiere, Hill’s mother said, “I don’t get why funny about those pictures. You look gorgeous.”

Presidential neologisms

There was a line in the film about Abraham Lincoln inventing the word ‘tits’, but it didn’t make the final edit.

Spielberg

According to co-director Phil Lord, a brief scene involving a foot squashing a face nose won the admiration of Steven Spielberg. It was, he said, the director’s favourite sequence.

Ice Cube

The former rapper Ice Cube delivers a particularly fine performance as a stereotypically shouty police captain, and gets some of the movie’s most memorable lines. Curiously, for an actor required to scream all kinds of obscenities, he was quite specific on what he would and would not say. On a set where improvisation was encouraged, Hill asked Mr Cube if he’d utter the line, “You can gargle my nutsack”. Ice flatly refused.

Fake members

On the topic of the genital region, one brief scene (which we shall be as vague about as possible, to avoid spoilers) involves a detached penis. Said member, the filmmakers reveal, was actually half a banana purchased from a local shop, with a touch of stage blood applied. The result is surprisingly realistic.

Sleepy doves

One scene sees Channing Tatum’s character step triumphantly from a limousine accompanied by John Woo-style white doves. Curiously, the birds had to be added in post-production due to the stresses of the sequence’s night time shooting schedule; the doves were asleep (“from flying around all day”, Hill notes), and their handlers wouldn’t allow them to be woken up. This scene, the commentary reveals, was achieved in a single take, with Tatum simply improvising bizarre lurches, tootles on instruments and raving utterances as he went along – the sublime, triumphant line involving one Miles Davis was made up on the hoof. A moment where Tatum abruptly throws up on Jonah Hill’s arm was also Tatum’s idea; according to Miller and Lord, he came up with the idea on the last day of the first week’s shooting, and filled his mouth with a mixture of oatmeal and water. Hill had no idea what was about to happen, and his horrified reaction to the stuff hocked up on his arm was genuine. In the commentary track, it’s revealed that Parnell originally said something very different here; at the time of filming, the line was actually “Doing cocaine with Whitney Houston’s niece”. Unfortunately for the filmmakers, Houston tragically died after production had completed – in fact, 200 prints had already been churned out with the now controversial line in place, and had to be hastily put aside. Parnell was therefore called back in to overdub something – anything – which would fit his lip movements in the original footage, and “Willy Nelson’s horse” happened to be a perfect fit. According to Jonah Hill, several other sentences were tried out, too, including the rather disturbing “Charlton Heston’s hearse.” Follow our Twitter feed for faster news and bad jokes right here. And be our Facebook chum here.