Momeyyy...how are we moving backwards?

Last week i was in London and i decided to take a one day trip to the beautiful town of 'Bath'. My cam round my neck, guided voice clips on my ipod and a map in hand i took the train and went. The city of bath is a UNESCO World Heritage Site. The combination of beautiful Georgian architecture and stunning scenery made it all so worth the trip. I started my day with a 4 hours spa at the Thermae Bath Spa. Spent 2 hours at their rooftop pool, filled with the naturally warm (very warm), mineral-rich waters which the Celts and Romans enjoyed over 2,000 years ago. Then followed 2 hours of massage and exfoliation and all the pampering stuff. After a full relaxation i headed to Sally Lunn Bun's, recommended by my colleague Ray. Basically, it is a bakery that Ms. Sally open in 1968 and few years later her secret recipe for buns was rediscovered and they re still produced till this day. Very much worth a taste!
Then i just walked around enjoying the scenery and the music festival and the exquisite architecture. I met many tourists, one interesting old man who kept on telling me sayings by Wiliam Churchil, one of which i still remember:
In the middle of an argument, a lady said to Mr. Churchil:
-Sir, if i were your wife i would not think twice about poisoning your drink
Then he replied:
-Madam, if i were your husband i would want that very very much!

On my way back, a mother with 2 kids, aged 7 and 12 i would say, were sitting behind me. The train was moving in opposite direction to how we were sitting, so the 7 years old asked his mom: "Mommey...how are we moving backwards?"

His question kept me thinking the whole trip back to London. I was asking myself, if my own kid asked me this question, how would i answer? Had he asked "why" are we moving backwards, i would have said "because we are sitting in opposite direction". But the kid asked "HOW"...and i just couldn't find an answer...Then, for the next few days, in the bus and in the tube, i paid attention to little children around me and listen to their questions... and i found that to be so entertaining, intriguing and sometimes a riddle like questions!