FIG. 1 is a perspective view of a pet toy design; FIG. 2 is a top view of a pet toy design; FIG. 3 is a right side view of a pet toy design; FIG. 4 is a left side view of a pet toy design; FIG. 5 is a front view of a pet toy design; and, FIG. 6 is a back view of a pet toy design. The broken lines illustrate a boundary, are for illustration only and form no part of the claimed design.