I claim the ornamental design for a vest for an animal, as shown and described.
FIG. 1 is a top, front, right perspective view of a vest for an animal showing my new design in a condition of use;
FIG. 2 is a top, rear left perspective view of a vest for an animal of FIG. 1;
FIG. 3 is a top plan view thereof; and,
FIG. 4 is a left side elevation view thereof, the right side elevation view thereof being a mirror image.
The fastening straps are shown with symbolic breaks in their lengths. The appearance of any portion of the article between the break lines forms no part of the claimed design. In the drawings, the broken line showing on the vest for an animal depicts stitching and forms no part of the claimed design. In FIG 1. the broken line showing of a dog depicts environmental subject matter only and forms no part of the claimed design.