1) They'll step in dog mess.
2) They'll trip over piles of carefully wrapped and color-coded recycling garbage bags (there are no residential and not many commercial garbage cans in the heart of the city).
3) They're not tourists with cameras and/or money wallets hanging around their necks.
4) They'll stumble on the cobblestones (that was me)!
But if you look up every now and then, you're bound to see the most amazing architecture, colorful window flower boxes, larger than life cartoon murals and of course, the Belgian flag (among others) blowing in the wind. Just be forewarned - there are a LOT of dogs in this city!