Joaquin Phoenix’s transition from lauded actor to showbiz curiosity gathered pace last night when he made a shambolic appearance on The David Letterman Show.

After perplexing fans recently by announcing he was quitting acting to become a hip-hop artist, the 34-year-old appeared on the chat show to promote his last film, Two Lovers, but gave only stammering one-word answers.

At one point, he pulled a wad of chewing gum from his mouth and stuck it to the host’s desk.

Letterman welcomed him with a glowing introduction and initially worked hard to coax answers out of the unresponsive star. But after receiving a raft of one-word replies, the presenter, known for his cutting wit, gave in to the live audience’s disbelieving laughter and began mocking the unkempt-looking Phoenix.

Taking aim at his shaggy beard, he enquired: “What can you tell us about your days with the Unabomber?”

Phoenix, who has been nominated for two Oscars, appeared vaguely offended but went on to take questions about Two Lovers, which also stars Gwyneth Paltrow.

Asked if it was correct that the film was based on a book by Fyodor Dostoevsky, he replied: “I don’t know.”

When told it says so in the opening credits, he responded: “Does it? I haven’t seen the movie.”

An increasingly disbelieving Letterman went on to broach Phoenix’s career change, which some believe is an elaborate hoax for a Hollywood mockumentary.

Asked if he would ever act again, Phoenix said: “Never say never, right? I don’t know. I don’t know what will happen.”

“But you’re not going to act anymore?” Letterman probed.

“No,” replied Phoenix.

“Why is that?”

“I don’t know,” the star responded.

Phoenix initiated only one exchange, when he zeroed on in a barely visible blemish on Letterman’s hand. “Are you alright? What happened to your thumb?’ he enquired.

The odd question sent the audience into fits of laughter, which only became louder when Letterman replied: “It’s just a little cuticle mishap.”

At one point, the frustrated host told Phoenix off for chewing gum, prompting the star to pull the wad from his mouth and stick it to the underside of Letterman’s desk.

Despite an increasingly tense atmosphere, Phoenix said he would like to come back on the show to unveil some of his hip-hop tracks.

“That seems unlikely,” Letterman replied, before closing the interview with: “Joaquin, I’m sorry you couldn’t be here tonight”.

Phoenix’s unusual behaviour began last November when he announced he was quitting acting for music. It was assumed he had been inspired by playing Johnny Cash in the hit film Walk The Line.

But last month, a video of the star rapping was posted on YouTube. After watching his talentless performance, in which he fell from the stage, fans assumed it was a joke.

The constant presence of a film crew, led by Casey Affleck, has added to rumours that the career change is merely a PR stunt.

Phoenix, however, insists Affleck is making a documentary about his transition from acting to music and that he is serious about his new career.

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