Daniel Radcliffe was left crippled with nerves when he agreed to tackle the fast-paced lyrics to Blackalicious hit Alphabet Aerobics on comedian Jimmy Fallon's U.S. late-night show earlier this week (beg27Ovt14) after learning the rappers would be watching.

Stuck for something fun to talk about during his segment on the show a few months ago, the Harry Potter star confessed he'd perfected the art of memorising difficult hip-hop lyrics and when he revealed he knew all the words to Alphabet Aerobics, Fallon's house band The Roots urged him to perform the track.

Radcliffe refused, but when he returned this week, he decided to give it a go.

He says, "Fallon said, 'The Roots really want to do it with you', so I was like, 'Ok!' But after I did the rehearsal and (drummer) Questlove came back into the dressing room, he said, 'Yeah man, I'm gonna text those guys (Blackalicious). They're gonna be really excited. I produced their second album'.

"I was like, 'Oh, Ok, you are friends with these guys!'. So I might not have been as bold to suggest it (the rap) had I known that. But I'm amazingly glad I did it. I was shaking with adrenaline a couple of minutes after; it was awesome."