A clever video puzzle to keep your brain active on a Friday. You’re a wizard and you’re making a potion. It needs to be stirred after exactly 45 minutes, no earlier and no later, or else it will be ruined. You have no clock or timer, but you do have two fuses of irregular consistency, each of which takes one hour to burn from one end to the other. How do you know when to stir your potion? Pause the video at the 4:30 mark if you don’t want to hear the answer.