LOS ANGELES

HOW skilled a secret keeper is Benedict Cumberbatch if he readily confesses the easiest method for extracting secrets from him?

Asked somewhat frivolously for information about one of the many coming projects he cannot talk about, Mr. Cumberbatch, the 35-year-old British actor, offered an equally facetious response.

“You could stick a knife in my thigh, and I wouldn’t tell you,” he said a few weeks ago, relaxing on the deck of the Venice, Calif., home where he was staying. But he added: “Pull the hair on my head the wrong way, and I would be on my knees begging for mercy. I have very sensitive follicles.”

Deeper still within his head were numerous vital details that Mr. Cumberbatch’s work required him to keep locked away. There was not much he could say about his dual roles as a necromancer and a talking dragon in Peter Jackson’s film adaptation of “The Hobbit,” and even less about the part he was shooting in J. J. Abrams’s sequel to “Star Trek.” (“I’ve got to be a complete and utter tease,” he said, more gleeful than apologetic.)