From Creatures Wikia
There were actually two Christmas Puddings made by Cyberlife:
Christmas Pudding 1997
If any Norn attempts to sneak a quick bite, the pudding will be a bit painful. The pudding will decrease in size when eaten. Also, your Norn may be lucky enough to find a surprise silver coin inside a portion. It's not all good news though; your Norn may have a lucky coin but he'll also have a sore mouth!