It's a great game, here's how you do it
Pairs of people, the caller and the reciever for lack of better terms.
The reciever chooses a range of numbers from 0 to x, these are the odds
As an example we will have the reciever pick 0 to 5
After the caller makes a 3 count both players call out a number each from within the current odds range. (ex: 1, 2, 3, 4, 5 • 0 to 5)
If both players call out the same number the reciever has to skull their drink
If the numbers are different, the players swap receiver/caller roles and reduce the odds by 1 (ex: 0 to 4)
Repeat steps until impossible odds (0 to 1)