But Swedish researchers Mats Amundin and Christer Blomqvist hope to prove Dino has said something cheeky to Flip before turning tail. Interpreting dolphin-speak is no easy task, as the animals make no face or body movements when emitting a noise.

But a specially designed recording device, attached by suction cups to Flip's dorsal fin, proves Dino has fired a volley of high frequency clicks, out of the range of human hearing, directly at Flip.

Amundin and Blomqvist have found these clicks, transmitted in a narrow sound beam, are used when a dolphin wants to say something specific to another animal, be it aggressive, flirtatious or maternal.

"The click sound may be a substitute for all the expressions we have in our faces as dolphins cannot portray these emotions in their faces or bodies,"said Amundin, zoologist at the Kolmarden Animal Park, 160 km south of Stockholm. "This is the first time we have been able to demonstrate that very high frequencies are used as social signals," he said.

For about 40 years scientists have known that dolphins communicate using whistles and clicks. They use different whistle alarms depending on what predator is approaching and use clicks for echo location in dark or murky water to find food or the coast, the sea floor and boats as far away as 800 metres (yards).

To date most research has concentrated on whistles, which lie in the human range of hearing, and has found each dolphin has an individual or signature whistle.

"But through whistles we have no idea of the dolpine's moods," said Blomqvist, a marine biologist taking his P.hd at Sweden's Gothenburg University. "To understand communication you really have to know who is saying what and to whom. We are still working on ways to tell the exact frequency and record the full band width but we are able todistinguish between sounds under and over 100 khz," he said.

A key feature of the research at Kolmarden, which has carried out dolphin studies since 1994, is that Amundin and Blomqvist are not trying to monitor the dolphin that is talking but the animal being spoken to.

The electronic recording device on Flip's back, designed over the past two years, records all the noises directed at him and video cameras located above and in the pool film the activity accompanying this noise to check the speaker.

"We have started to see a lot of click sounds during aggressive interactions," Blomqvist said. "Maybe dolphins use click sounds in aggressive situations because they can be directed. You don't want to get on the wrong side of the big guy or your friend. We need to see the kind of behavioural situation where these sounds are used and how they differ to be able to interpret what is going on," he added.

His next step will be to research communication between dolphins in their own environment with plans for astudy at Sarasota Bay in Florida next year.

Although analysing high frequency clicks is a major step in the mystery of dolphin-speak, Blomqivst is the first to admit that there is a long way to go before humans can understand what dolphins are saying.

"This is just one piece of the jigsaw to try to see the whole picture," Blomqvist said.