Came across this in my notes from a few years back, quoting an interview with Christopher Walken in the New York Times.

When he first started in film, Walken would immerse himself in researching a role, but it didn't take. Instead, he adopted a novel line-reading technique. When he received a script, Walken would immediately cross out all the punctuation. Nowadays, he no longer has to mark up the pages he just doesn't see full stops or commas any more. 'It lets you decide what the important word is,' Walken says. 'It might be the noun, it might be the verb. It might be a word you never thought of.'

Walken also does his lines in various voices. He gives me an example. He pretends he is going to the gas chamber and says, 'I don't wanna die.' First, he does it straight, then in what he calls his 'Mamma mia what a pizza' voice, followed by that of a Gestapo officer and, finally, in one of his favourites, Bugs Bunny. 'That's why I love listening to people with accents,' Walken says. 'They're always emphasising the wrong word, and it makes me think.'

 Searching for the above online I then chanced upon this:

"Sometimes," says Walken, "in a scene, without telling the other actor, I'll pretend that I'm Elvis. I'll just pretend I'm Elvis and the other actor will not know. And it'll make me smile. Or even just smile inside. I'm doing Elvis and this guy doesn't know I'm doing Elvis. I do it when things are getting stale. I'll do it to, like, juice things up a little."

 The full New York Times interview from 2004 is here. And the other one (from The Guardian, in 2003) is here.