I claim the ornamental design for a staircase for animals, as shown and described.
FIG. 1 is a perspective view of the staircase for animals:
FIG. 2 is a front view thereof;
FIG. 3 is a back view thereof;
FIG. 4 is a top view thereof;
FIG. 5 is a bottom view thereof;
FIG. 6 is a side view theoref; and,
FIG. 7 is a side view thereof showing the side opposite that shown in FIG. 6.
The broken lines shown in the drawings show portions of the staircase for animals and environmental structure that each form no portion of the claimed design.
The broken away symbols in the drawings indicate the appearance of any portion of the article between the break lines forms no part of the claimed design.