How to make people disappear

This is a shot of Cardiff Central train station taken at twenty five minutes past five on a Monday evening (see the clock!) There were actually LOTS of people around but the 2 second exposure I used has meant that anyone walking has virtually disappeared and only the people left standing have been captured by the camera.

If you look very closely at where the darker foreground meets the lighter pavement, you can make out the legs of people passing by.

Now for my next trick.....