And then I put on Doctor Who. It was a punt – my son was eight and he liked science. We went in at the David Tennant era – beginning with the episode The Christmas Invasion, where the Doctor doesn’t wake up till a third of the way through the episode. Suddenly there, standing in his pyjamas with a big boyish grin, was Tennant, describing a frightening alien with a weapon as a “big fella”. My son grinned back at the screen. When Tennant’s Doctor arrives properly, he barely stops talking or moving. He’s sword-fighting, then joking, then forgiving – and then he kills the baddy with a satsuma. All while repeating certain phrases to himself. My son laughed in recognition (he often repeats phrases to himself). He turned to me, eyes wide.