BoS is a reaction game similar to snap, except with more players and subtantially more drinking.
BoS (or just "buckets") is played with a shortened deck, with no jesters and four cards more than the number the players require (although an eight card drittsekk has been known to work with a sufficiently large number of players). Fives are included in the shortened deck - hence with five players the fives, aces, kings, queens, jacks and tens will be in play. The game is best played with a small number of people (4-8).
Each player is dealt four cards, and the remaining cards in the deck in play are placed in the centre of the playing area as a target (some variations have no target). All drinks are best cleared from the playing area.
The dealer then calls "three...two...one...pass" (with an even tempo, and about two seconds spent over the whole, although the rate tends to increase as time passes in a given hand), and at the moment of "pass", each player must pass one card to the next player in the direction of the deal. If at any point, including at the start, a player has a winning hand, he may put his hand on the target (if present - just on the table if not). The other players must then place their hands on top of the lowest player, and the last player to put his hand on the pile has to drink a double fine (i.e. two fingers, traditionally). The winning player then deals the next hand.
A "winning hand" is either four cards of the same numerical value, or a straight flush (cards of consecutive increasing value in the same suit). Bluffing is allowed - some (not all) variants allow hitting the target so long as you're not pinned their by the other players, and if there is a target then hitting the table beside the target is also reasonable. However, being the player with his hand on the target and not having a winning hand (known as "revoking") will invoke a half pint fine.
Fives are a complication. If a player wins with four fives, all the other players must drink a pint fine (some variants are more lenient). However, each five you have in your hand at the time a hand finishes is worth a fine. An optional rule is that three fives in a player's hand requires that player to buy a round of whisky, although a pint (or even half pint) fine is sometimes considered a valid substitution. Hence fives often get passed on, and four fives are relatively rare.