Plop is a two-part installation on the Google Bridge that engages both the vehicles traveling below and the Googlers walking through the bridge.  

For the Bridge-User:  When a user approaches the bridge entrance, a Kinect (or similar device) detects their face (probably using google data) and uses that image to perform a reverse image search.  The number of hits for this search is then sent to the computer, which translates the data into the scaling of "ripple" graphics.  As the user crosses the bridge, a second camera tracks their footsteps, which are marked by a "rippling" effect across the floor, scaled to the user's "relevance" according to Google data.  

For the Under-Bridge Traveler: Have you ever wanted to emphasize how fast your car is going by advertising it to the whole of East Liberty on a Google bridge?  Well, if you have, Plop has got the installation for you.  As your vehicle approaches the bridge speed-detecting devices to measure your speed.  This data is then used to calculate both the size and the speed/blur of the giant "Zoom!" graphic which will skrrrttt into view on the bridge above, thus displaying your bravery (or stupidity) to the people around you.