I googled it for you!
Punts
A punt, also known as a kick-up, refers to the dimple at the bottom of a wine bottle. There is no consensus explanation for its purpose. The more commonly cited explanations include:[1]
* it is a symbol -- the larger the punt the better the wine
* it is a historical remnant of old-fashioned glass-blowing techniques; by raising the point where the glass-blowers tube is attached, the small imperfection would not scratch the table
* it had the function of making the bottle less likely to topple over -- a bottle designed with a flat bottom only needs a small imperfection to make it unstable -- the dimple historically allowed for a larger margin of error
* it consolidates sediment deposits in a thick ring at the bottom of the bottle, preventing it from being poured into the glass;[6]
* it allows a bottle of sparkling wine to be turned upside-down and then stacked (depending on its shape)
* it increases the strength of the bottle, allowing it to hold the high pressure of sparkling wine/champagne
* it holds the bottles in place on pegs of a conveyor belt as they go through the filling process in manufacturing plants
* it accommodates the pourer's thumb for stability and ease of pouring
* According to legend the punt was used by servants. They often knew more than their master about what was happening in town, and with a thumb up the punt they could show their master whether a guest was reliable or not. (Vinavisen 19 may 2008 - danish)
* it provides a grip for riddling a bottle of sparkling wine manually in the traditional champagne production process.
* it simply takes up some of the volume of the bottle, giving the impression that you're getting more wine for your money than is actually the case
* Taverns had a steel pin set vertically in the bar. The empty bottle would be thrust bottom-end down onto this pin, puncturing a hole in the top of the punt, guaranteeing the bottle could not be refilled [folklore]