When Selsden and Malloy try to open Lady Penelope's safe, Malloy's torch begins to smoke - the torch bulb has become so hot, it has started to set the prop alight.
At around 41:00, Thunderbird 1 can clearly be seen wobbling on her support wires. Not at all common for this series.
Just as the villains' car goes out of control in the opening sequence, a huge lump of greenery falls out of the sky in the background.
In one scene, Lady Penelope is reading a telegram. However, the UK's inland telegram service was withdrawn in 1982, about 80 years before this episode is set. (Note - At the time of the episode's original airing in 1966, the telegram service was still in use.)