I still felt like it was one of the best labs I've ever done.
The timer counted down until the end of the lab period; the student needed to cut each wire to stop the detonation. The original goal was to post to Twitter when a student made a mistake but we didn't get it implemented in time.
Here's the binary itself: http://www.cs.rpi.edu/academics/courses/spring10/csci4971/re...
http://www.cs.cmu.edu/afs/cs/academic/class/15213-f05/lectur...
I still felt like it was one of the best labs I've ever done.