Pop rocks!

Nope.  Not that kind.  Rather this kind (see below).  Note the small rocks perfect position at the edge of the bike lane (in this case on Mill St.).  Now don't get me wrong.  These don't pop your tire, rather if you hit them just right with the edge of a moderately well inflated front wheel, they will shoot (pop) out the side.  Sometimes they really go and shoot out into the vehicle lane. 

If your timing is just so, you might even get a satisfying ping as the pop rock connects with a vehicle that is a bit to close to the bike lane.  I'm not encouraging you to use pop rocks as convenient projectiles to tame vehicle traffic.  However, it is very likely that a vehicle had a role in depositing the pop rock in the bike lane (along with other detritus).  Really, all we're doing is returning said material to the location it originated from.

It is a rather fun riding game.  See if you too can master the pop rock!