The ornamental design for a frog-shape teacup, as shown and described.
FIG. 1 is a perspective view of a frog-shape teacup;
FIG. 2 is a front side view of the frog-shape teacup shown in FIG. 1, the rear side view is a mirror image of the front side view and this is not shown;
FIG. 3 is a left side view of the frog-shape teacup shown in FIG. 1;
FIG. 4 is a right side view of the frog-shape teacup shown in FIG. 1;
FIG. 5 is a top view of the frog-shape teacup shown in FIG. 1; and,
FIG. 6 is a bottom view of the frog-shape teacup shown in FIG. 1.
The broken lines shown in the drawings depict portions of the frog-shape teacup that form no part of the claimed design.