WHEN Caroline Costello heard a crunch while eating an oyster, she feared the worst.

She immediately spat it out, expecting to see half a molar on her plate.

But to her surprise she found not one, but two oyster pearls.

She said: "Whether I'm eating chicken or fish I always manage to get a bone. I thought 'here we go again', I just presumed it was a piece of shell or my tooth breaking.

"When I spat it out on the plate and saw it was a pearl I couldn't believe it. I carried on eating the same oyster and the same happened again."

Miss Costello, 33, and fiancée Mark Jupp, 37, had been to La Poissonnerie fishmongers, in Brighton Road, Shoreham, to buy a batch of oysters and champagne to celebrate moving into their new home in Graham Avenue, Portslade.

Builder Mr Jupp said: "We have been together for four years and it is our first home we have owned together. We wanted to have a celebration of sorts so I cooked the oysters with parmesan and we sat down with a bottle of champagne.

"After we found the pearls I went back to the fishmongers and told them. They had never heard of it before, a million to one chance."

Not only did Miss Costello find two pearls in the one oyster - but they were also different colours.

The black pearl in particular is rare and is usually only found in oysters from the South Pacific.

Kerry Duckhouse, curator at Brighton Sealife, explained pearls are formed when a foreign body slips in between the mantle and the shell - which irritates the oyster.

If the oyster cannot get rid of it, the mollusc coats it in a substance called nacre - which is the same material it uses to create its shell.

It results in a pearl which can come in a variety of colours including white, grey, red, blue, green and black.

She added: "Oysters are farmed these days for pearls whereby sand and other substances are pumped into the oyster.

"Even then only 50 per cent of the farmed oysters produce pearls as they usually manage to get rid of whatever it is. So to find a pearl in an oyster which has been caught at sea is very rare."

The couple are yet to get the two pearls properly valued, although one Brighton jeweller told The Argus they could be worth up to £1,000 depending on the quality.

Ms Costello added: "I would like to get them made into some form of jewellery, it is certainly a good omen for our new home anyway."