James Franco badly injured his head whilst filming 'Pineapple Express', his co-star Seth Rogen has revealed.

Rogen starred in and co-wrote the 2008 comedy action movie and he and Franco switched parts during the initial script read through with him taking on the role of stoner Dale Denton and Franco as his drug dealer Saul Silver, who find themselves fleeing corrupt police and hitmen after witnessing a murder.

Rogen, 36, has been reminiscing about the flick to mark the movie's 10th anniversary and sharing some secrets from the set with his 7.61 million Twitter followers.

The 'Superbad' star revealed that Franco's only wore a headband as Saul for a scene in the woods because he had suffered a nasty cut, which needed stitching up after running into a tree which had screw through it.

Rogen wrote: ''The reason Saul wears a headband in #PineappleExpress is the result of another injury. There's a shot (that's in the movie) when we are running through the woods, Franco hits his head on a tree. He actually hit his head on a screw that was holding a pad in place and got stitches. (sic)''

The 'Knocked Up' actor and his co-star Danny McBride (Red) also got into a bit of bother on set, the former broke his finger and the latter had his head sliced after Franco hit him, all in the same sequence.

Rogen shared: ''Throughout the fight scene in Red's house in #PineappleExpress, I broke my finger and Danny McBride got his head cracked open when Franco hit him with the bong. (sic)''

He also revealed that Red was meant to die the first time he was shot, but because his character was ''so funny'', they kept the drug dealer in it for longer.

He wrote: ''In #PineappleExpress, Red was originally supposed to die the first time he was shot when he was tied up in his apartment, but we thought Danny McBride was so funny that we just kept bringing him back to life. (sic)''

Rogen also revealed that he and the film's other writer Evan Goldberg ended up rolling around 100 marijuana joints one day, because none of the other crew members knew how to do it.

He said: ''In #PineappleExpress, me and my co-writer Evan had to roll all the cross joints needed to film (about 100) ourselves because nobody else on the crew could roll them properly. (sic)''

Rogen also claimed that they had planned on Red reaching his demise in a Ford Fiesta, but the automobile makers refused because they didn't want one of their cars ''involved in a movie murder''.

Luckily, Daewoo didn't have a problem with their Lanos model being used for the stunt.

He added: ''In #PineappleExpress, originally, Red killed Matheson with a Ford Fiesta, but Ford didn't want their car involved in a movie murder so we had to change it to a Daewoo Lanos, which is ultimately much funnier I think. (sic)''