The game board is ring-shaped and depicts a calendar, i.e. fields for each month. The players put their pieces in their birth month; Klaus the mouse starts in the current month. The playing pieces are birthday cakes (Klaus is an actual mouse). Eleven picture tiles are placed openly into the center of the board.
The active player first checks whether there are any gifts under his/her cake. If so, the player has to say which month the gift(s) belong(s) to - if right (the color code on the backside tells the answer), the player can keep the gift. If wrong, the player has to put the gift under another player's cake.
Afterwards, Klaus is moved by a die. The active player picks a tile from the middle that matches the month Klaus moved to and keeps it (if there is no matching tile or the player makes a mistake, the tile is given away as above). When Klaus passes a player, he gives that player another tile as a gift.
When all tiles have been distributed, the player with most tiles is the winner.
(User summary by HilkMAN)