Not every piece of glass started in the Glass Lab makes it into the annealer. A crash on the other side of the room usually means that something has gone wrong and a piece has hit the floor. The sound of cracking as you are heating up in the glory hole can mean that in a minute you will be fishing a mangled piece of partially molten glass out of the hole with whatever has remained on your pipe. If you aren't breaking or losing a few glassworks every once in a while you probably aren't trying hard enough or aren't learning anything new.