Place a small bowl that has a rim on the bottom upside down inside of a larger bowl.  Rest the bottom of a shucked corncob inside of the rim of the small bowl.  Using a sharp chef's knife, slice the kernels off the cob, cutting top to bottom.  The loose kernels should be contained in the larger bowl, reducing the mess.  Rotate the cob and repeat until all the kernels are sliced off the cob.