Force through food chopper enough carrot to make 3/4 cup. Put into saucepan with butter and onion, and cook 10 minutes or until brown, stirring frequently. Add flour and when smooth add 1 cup boiling water in which is dissolved vegetable or beef extract, and stir until sauce boils. Add salt, pepper, lemon juice and cayenne. Remove meat from lobster and cut in pieces the size of scallops. Place oysters in strainer over bowl and rinse with 2 tablespoons cold water, reserving all liquor. Pick over oysters to be sure that there are no pieces of shell adhering to them, add oysters to liquor, and cook them until the edges curl. Drain, reserving both liquor and oysters, and in the liquor cook scallops 5 minutes or until tender. To the oyster liquor add cream to make 1 cup; add to the sauce and bring to boiling point. Add oysters, scallops, and lobster and serve very hot, garnished with bits of pimiento and truffles or ripe olives.