Lap dancer ovulation, the mental state of plants, and the question of whether Coca-Cola is an effective spermicide highlighted the annual Ig Nobel Prize ceremony at Harvard University Thursday.

Awarded since 1991 by the magazine Annals of Improbable Research, which is loosely affiliated with Harvard, the Ig Nobel awards honor "achievements that first make people laugh, and then make them think." Past winners include Dan Quayle and ducks that practice homosexual necrophilia (or at the least the scientists who study such ducks).

(View a slideshow of 2008 Ig Nobels winners.)

Scientists who discovered that professional lap dancers earn higher tips when they enter their fertile periods were awarded the coveted Ig Nobel economics prize on Thursday night at Harvard's Sanders Theatre, during a ceremony in which prizes were handed out by an actual Nobel laureate – William Lipscomb, who won for chemistry in 1976. Lipscomb, 89, was also the "prize" during the "Win-a-date-with-a-Nobel-laureate-contest."  (View a slideshow of past Ig Nobel winners.)

Winners were given a maximum of 60 seconds to deliver an acceptance speech, but will be permitted another 5 minutes to explain themselves during free public lectures on Saturday at the Massachusetts Institute of Technology. Seven of the 10 winners attended the ceremony Thursday at their own expense.

The chemistry prize went to American researchers who discovered that Coca-Cola is an effective spermicide, and also to a competing team of Taiwan researchers who discovered that it is not. The Peace prize, meanwhile, was awarded to Switzerland for adopting the legal principle that plants have dignity.

Here is the official list of winners, text courtesy of Improbable Research:

NUTRITION PRIZE
Massimiliano Zampini of the University of Trento, Italy and Charles Spence of Oxford University, UK, for electronically modifying the sound of a potato chip to make the person chewing the chip believe it to be crisper and fresher than it really is.

PEACE PRIZE
The Swiss Federal Ethics Committee on Non-Human Biotechnology and the citizens of Switzerland for adopting the legal principle that plants have dignity.

ARCHAEOLOGY PRIZE
Astolfo G. Mello Araujo and José Carlos Marcelino of Universidade de São Paulo, Brazil, for measuring how the course of history, or at least the contents of an archaeological dig site, can be scrambled by the actions of a live armadillo.