What happens if you swallow glass?

That shard of glass would travel through your oesophagus, stomach, approx. 8.5 metres of small & large intestine, through the colon and out the rectum. A pretty painful process. Depending on the size/shape/luck of the glass, you could also cause an internal tear and internal bleeding. The tear could be hard to diagnose. You'd probably also have to have exploratory surgery to locate the perforation (I hope for your sake it's not near the colon!), then have it fixed up (assuming they could find it), then spend a while in hospital and pay a mega-load of hospital bills.

So, I'd recommend not swallowing glass.. For your own safety.

That being said, if you already have swallowed glass, get yourself to the hospital, tell the ER doc what you've done and how long ago you did it. The faster they find it, the more likely it is that you'll get away with not too much damage.