The ornamental design for a teether, as shown and described.
FIG. 1 is an upper, front, right perspective view of a teether showing our new design.
FIG. 2 is a lower, front, left perspective view thereof.
FIG. 3 is a front elevation view thereof.
FIG. 4 is a rear elevation view thereof.
FIG. 5 is a left elevation view thereof.
FIG. 6 is a right elevation view thereof.
FIG. 7 is a top plan view thereof; and,
FIG. 8 is a bottom plan view thereof.
The ornamental design which is claimed is shown in solid lines in the drawings. The broken lines depict portions of the article that form no part of the claimed design.