Why does water in a wine glass invert the background pattern?

[void_2]

Hello, I came across something interesting on the internet. I saw an image in which a wine glass was half filled with water and put in the middle of the two different colored backgrounds. In the air portion within the glass, the two backgrounds were visible through the glass, however; in the water portion, the opposite backgrounds were horizontally visible, this resulted in a checkered pattern visible in the wine glass. If my description was puzzling then this image should help http://www.thinkstockphotos.com/image/100408932. I tried this myself and it worked, so my question is what causes this effect. My initial hypothesis was that the shape of the glass with the water resulted in some type of concave mirror that horizontaly inverted the light causing the effect. I am not entirely sure about this but I do know that the unique shape of the wine glass is a factor as this effect is not possible with a regular glass filled with water. Some assistance is appreciated, thanks in advance.

 

[Andy Resnick]

Nice optical effect. It's nothing more than refraction- the glass stem and water-filled bowl act like a lens- note how the 'air filled' part of the bowl does not reverse the colors.