The King of Diamonds Affair - S2-E25
Revealing mistake: When Solo and Illya, posing as maintenance workers on the London street, are opening the manhole to go underground, two cars - a blue VW hatchback and a white roadster - pass them twice going in opposite directions each time. And while most of the cars are driving appropriately on the left, one pulls up behind them driving on the right (which is to say, wrong) side of the road. (00:13:00)
Answer: He must have ridden in an Eaton's store elevator while he was in Canada at some point. For some reason, this elevator reminds him of it. The show's original concept had Solo being a Canadian, so this may be a minor nod to that fact.
raywest ★