I'm sure some of you academics out there know what's up with this, but I had to take to Wikipedia to see what the hell this was all about (since my head jumped to a piercing I won't mention).
Here's what Val said about it:
If you drop molten glass into water, it cools very quickly but has lots of residual stresses inside. It's very strong under compression (you can't break it with a hammer), but if you snap off just the tail, the whole thing explodes in a shower of tiny glass powder.
They ended up breaking this in lieu of the traditional Jewish breaking of the glass. I kind of love the symbolism of such a hard structure with such a fragile mechanism. Plus, SCIENCE! If you want to attempt this at your ceremony, just make sure to find a helpful scientist or science teacher to make it happen safely.
And check this shit out: these guys over at Smarter Every Day decided to film a slo-mo version of this kind of drop with a high frame rate camera. At 2:31 it turns into what looks like an explosion of rainbow confetti! Plus, they totally explain the science behind it for our braining pleasure.
Check out more photos of Val and Galen's science-loving wedding here.