Scientists who unlocked the inner secrets of dog fleas, crisps and tangled string have won prizes at the tongue-in-cheek Ig Nobel awards.

A light-hearted alternative to Scandinavia's Nobel Prizes for otherwise serious researchers, the prizes were presented at Harvard University in Massachusetts last night.

More than 1,000 people, including seven of the 10 'laureates', attended a ceremony that in irreverent spirit also featured sword-swallowing, paper airplanes, and an eight-year-old girl tasked with stopping boring speeches.

Three French scientists from the École Nationale Veterinaire de Toulouse took the biology prize for establishing that fleas living on dogs jump further than those resident on cats – 20cm further, on average.

Potentially more controversial was the work of an Italian-British duo who won the nutrition prize for their study 'Auditory Cues in Modulating the Perceived Crispness and Staleness of Potato Chips'.

The ground-breaking study first published in the Journal of Sensory Studies involved '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,' Ig Nobel organisers said.

The Ig event, produced by science humour magazine Annals of Improbable Research, honours the hair-brained efforts of a brainy profession in hope it can 'make people laugh, and then make them think'.

String mathematically proven to tangle

Winning an Ig is perhaps not every scientist's burning ambition. Winners even have to pay their own way to Harvard to accept the honour.

But after 18 years the event remains a hit among those who believe science needs a more popular image.

This year's physics Ig Nobel fell to US academics providing mathematical proof that hair, string, or anything else of the kind, will inevitably become tangled in knots - a process termed 'spontaneous knotting of an agitated string'.

There was even more agitation over the chemistry prize, awarded jointly to rival teams - one from the US which determined Coca-Cola to be an effective spermicide and one from Taiwan which proved it is not.

The medicine prize was awarded to a team at Duke University in North Carolina who showed that high-priced placebos work better than cheap fake medicine.

A team at The University of Sao Paulo in Brazil won a special archaeology prize for showing how an armadillo can mess up an archaeological dig.

A team from the University of New Mexico, in the US southwest, ventured far from their desks for bizarre research that won the economics prize on the relationship between lap dancer's ovulatory cycles and earnings.

Plants have dignity in Swiss law

David Sims of Cass Business School in London won the literature prize 'for his lovingly written study 'You Bastard: A Narrative Exploration of the Experience of Indignation within Organizations',' the committee said.

Meanwhile, the peace prize - the most keenly watched in the real Nobel awards - was awarded to the people of Switzerland and their country's Ethics Committee on Non-Human Biotechnology 'for adopting the legal principle that plants have dignity'.

Handing out awards was William Lipscomb, the genuine 1976 Nobel laureate for chemistry, also doubling, at the age of 89, as the hero in the 'Win-a-Date-With-a-Nobel-Laureate Contest'.

The prizes themselves consist of dull plaques made up in keeping with the night's party theme - redundancy.

'This Ig Nobel Prize is awarded in the year 2008 to an Ig Nobel Prize Winner, in recognition of the Ig Nobel Prize Winners' Ig Nobel Prize winning achievement,' reads the plaque.

Previous prizes have been awarded to researchers who discovered that Viagra helps hamsters overcome jet-lag, studied how sheets wrinkle, and uncovered homosexual necrophiliac behaviour in the mallard duck.

Improbable Research publishes its magazine every two months and runs a blog on the website, which also hosted a live webcast of last night's ceremony.

In a wry comment, the website noted that Americans were presented with two events back to back 'that might be surprisingly similar' - the wacky science event, then the televised debate between vice presidential candidates Sen Joseph Biden and Gov Sarah Palin.

The winners of the real Nobel prizes will be announced over the next ten days, starting with the Nobel Prize for Medicine on Monday.