Looks can be deceptive...

A BMJ study by researchers from Cornell University found that the amount of drink a person pours and consumes can depend on the shape of the glass. It's a great example of how perceptual biases can influence behaviour. To quote the study:

"Variations in pouring and drinking behaviour mean that the amount of alcohol consumed from a mixed drink can vary widely. An important unaccounted source of bias in self reported consumption of spirits may have to do with the shape of the glass into which a drink is poured. Two of the most common shapes of glasses for spirits are elongated "highball" glasses and short, wide "tumblers."

In one study, adults poured 28% more breakfast juice into short, wide glasses than into slender ones holding the same volume. This is the result of two perceptual biases: people generally estimate that tall glasses hold more liquid than wide ones of the same volume, and they focus their pouring attention on the height the liquid reaches and insufficiently compensate for the width of the glass. [Even practice did not completely eliminate the tendency to overpour into short, wide glasses.] Despite an average of six years of experience, bartenders [in the experiment] poured 20.5% more into short, wide glasses than tall, slender ones; paying careful attention reduced but did not eliminate the effect."

More information on the psychology of food can be found here at the Food & Brand Lab at Cornell University.