I claim the ornamental design for a teether, as shown and described.
FIG. 1 is a top, front, right perspective view of a teether, showing my new design;
FIG. 2 is a front elevational view thereof;
FIG. 3 is a rear elevational view thereof;
FIG. 4 is a left side elevational view thereof;
FIG. 5 is a right side elevational view thereof;
FIG. 6 is a top plan view thereof; and,
FIG. 7 is a bottom plan view thereof.
The dash-dash broken lines in the drawings depict portions of the teether that form no part of the claimed design. The dot-dash broken lines in the drawings represent boundaries that form no part of the claimed design.