Robert Pattinson finds it hard to be spontaneous.

The 'Twilight' heartthrob admits he can't just do things on a whim and has to think about what he says and the consequences of his actions before he actually does them.

He said: "I just like doing things where you have a little time to think about what you're saying. I've always had a problem actually thinking before I open my mouth. Yeah, being spontaneous or just thinking. I have a problem with thinking."

The 24-year-old actor recently shaved his hair off and joked he had to do it because he had headlice, also known as nits.

He joked on 'The Ellen Degeneres Show': "It's three days old. I got a terrible infestation of nits and I had to shave it all off."

However, he soon reassured his army of females fans by revealing the real reason behind his new image was for his new movie 'Water For Elephants', which he begins filming alongside Reese Witherspoon later this week.

He said: "No, I'm doing a film. It's about a circus in the 1930s."

Robert will play a circus worker who falls in love with an older woman, the wife of an animal trainer.