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1) In Vietnam everyone and their brother will try to sell you a poncho as soon as it starts to rain. In New York, every other store will sell you umbrellas.
2) In New York you can duck into the subway to stay dry and get where you need to go. In Hanoi, You've got to throw on your poncho, roll up your pants and drive your motorbike.
3) In New York you're pretty sure lightning will hit a tall building with a lightning rod. In Hanoi, well, you might be that tall building.