Coke can full of Chem shuts down a Subway.

A soda can sets off police in the subway.

http://www.cnn.com/2005/US/10/07/newyork.subways/index.html

Comment: With a new treat about our subways ripe for attack, I feel it is only a matter of time before another Terrorist attack happens. With our forces tied up in a war and the hurricane troubles, we may not be prepared for the next one.