These bite-sized morsels make for tasty appetizers.
In medium saucepan of boiling water, cook shrimp until opaque and bright pink, about 3 minutes. Drain; rinse with cold water. Cut cooled shrimp into 1/4-inch pieces. In bowl, mix with corn, scallions, mayonnaise, lime juice, salt, and pepper. Chop 6 radishes into 1/4-inch pieces; stir into filling. Cover; refrigerate while preparing radish cups.
Cut thin slice off bottoms and tops of remaining radishes. Cut each radish in half crosswise. With melon baller, scoop out center of radishes, leaving 1/4-inch border. Fill each with a heaping teaspoon filling. Chill until ready to serve.
If you use fresh corn, blanch in boiling water for one minute; drain; rinse with cold water, then scrape off the kernels.