The minotaurs are always guarding a chest, in one of the 3 vertical spots behind them... And chests are always guarded by a minotaur! (View the kill screen).
When the chest is opened, they turn around to face the opened chest.
This information can be useful in circumstances. For example, if you find a minotaur, then you know that somewhere behind them is a chest. Many times you can safely figure it out and take a (safely) calculated gamble. It can also be useful from the other direction if you open a chest and see a "7" then you know there's a minotaur and a rat, for example.