Not only is this one of the most straightforward and appealing explanations of the TARDIS dimensional mechanics "(Which box is larger?), but it demonstrates Toms ease with exposition. From an actors point of view, it might be tempting to elucidate it in as lively a manner as possible but he reels off his lines in the matter-of-fact tone of someone whos lived in the TARDIS for generations. He captures a slight ennui, which feels right. Once more, it feels like he is the Doctor, rather than an actor playing the Doctor. His bored reaction to Leelas question about the yo-yo (Doctor, can I stop now? If you want to.) reflects that side of the Fourth Doctors character as well, and it also points to his disregard for her in a humorous way. That disregard wasnt entirely acting. Toms relationship with Louise Jameson, the actress who played Leela, was initially frosty. Although things improved between them, a certain tension does manifest itself on the screen. He rarely makes eye contact with her which is something he famously did with actors he disliked. Luckily, Toms aloofness makes sense in terms of the story here and theres a nice amount of understated comedy as well, proving that he was just as compelling in the quieter moments as he was in full-on Time Lord saviour mode.