The ornamental design for a toothbrush, as shown and described.
FIG. 1 is a right side elevational view of a toothbrush according to the invention;
FIG. 2 is a left side elevational view of the toothbrush illustrated in FIG. 1;
FIG. 3 is a rear view of the toothbrush illustrated in FIG. 1;
FIG. 4 is an enlarged bottom elevational view of the toothbrush illustrated in FIG. 1;
FIG. 5 is a first perspective view of the toothbrush illustrated in FIG. 1;
FIG. 6 is an enlarged second perspective view of the toothbrush illustrated in FIG. 1; and,
FIG. 7 is an enlarged third perspective view of the toothbrush illustrated in FIG. 1.
The broken lines in the drawings illustrate portions of the toothbrush that form no part of the claimed design. The bristle arrangement shown in dot-dash-dot broken lines is included for the purpose of illustrating the boundary of the claim and forms no part of the claimed design.