The parvis of ND is closed to traffic and the locals use it to hone their skating skills -- and they won't refuse a few Francs by way of your appreciation for a particularly awesome trick.  We saw a few of those, including some that seem, on reflection, to be more magic than anything else.

These three Parisii are travelling backwards at about 15mph (I'm guessing...  it was fast) and all six legs are scribing sine waves around the cups.  Of the 40-or-so cups on the street, they hit exactly zero.

A few minutes later they did it again...  with three legs.