Why did this happen? (science question)

[CardSharpCook]

So my roommate buys these two thai energy drinks and brings them home. They are warm. We put them in the freezer to make them cold. After waiting some amount of time, we remove the drinks from the freezer. They are still liquid. No ice has formed. He advises that I shake the drink. I do so and immediately the entire drink turns into an icey slush. I can't explain why this would happen. Can you?