Let's say you get called out to fix an ice maker that has frozen over. You show up at the job, open 'er up, and this is what you see:

Another angle:

What do you think happened here? What could have caused that kind of damage to the walls of this ice box?

Let us know what you think in the comments! Or, if you're stumped, you can read the topic this scenario comes from and learn how it happened yourself.