“I love it,” says Griffiths, 61, of working with fresh-faced actors like Radcliffe, whom he met while filming the first three “Harry Potter” movies (Griffiths portrays Potter’s evil Uncle Vernon). “I know I have this kind of teaching element in me, but I don’t want to become a ‘teacher of theater’ because that would formalize something that I’d much rather keep casual.”

Nonetheless, he speaks with near-parental pride about his “Equus” co-star. “I watched [Dan] grow up. And having spent six consecutive years filming, he probably has more elapsed time experience in front of a camera than almost any other actor in the country, including people like Sean Connery.”

Griffiths admits, however, that when it comes to the stage, “[Dan’s] a complete virgin.” To this end, he offered Radcliffe numerous theater tips, covering everything from taking a bow (“Feel it. Remember it. Savor it.”) to tackling the character of Alan Strang — a part Griffiths says he could never have done at Radcliffe’s age. “Not in a month of Sundays. I certainly lacked the emotional awareness that you need for it.”