It was rather uncomfortable for Percy to have this conversation in the back seat of a taxi while the driver was listening to everything that was being said. He cleared his throat, being embarrassed, then told Katie, "I'd rather not end the evening here, on such a low note. And it's a bit cold to go walking around the city. So, the cinema it is."
He leaned forward to tell the cabbie, "Please take us to the nearest movie theatre, please? I think there's one about four blocks from here."
Returning to his seat beside Katie, he told her, "How much do you know about Muggle movies? There's this one, still in the theatres, 'Lord of the Rings: Return of the King' that's very good, but it's the last in a three part series, and if you haven't seen the previous two films, it may be hard to follow? Otherwise... you may choose when we get there."
After failing so poorly at his last plan to take Katie dancing, he didn't want to risk her making another scene by choosing a film that she didn't want to see.