Zac and I have heard this phrase so many times this week that it has become a running joke. Whenever one of us messes up, the other one says, "Mind the gap." We hear the expression at least 100 times a day while riding the tube. Sometimes the train station platform is not completely level with the train itself, leaving a high step, or a gap of several inches. For those of you following along in "American," the warning means to watch your step. We have found that the phrase applies nicely to all sorts of situations with which we are intimately familiar: spilling drinks, dropping coins (which happens a lot because I have to stare intently at every coin to determine its value), to actually making a misstep. Yesterday while staring intently at a landmark, I failed to "mind the gap," stepping off a curb and nearly falling. But that was yesterday. Today we began at Tower Hill, looking out at the infamous Tower of London. The sky was uncooper...