We claim the ornamental design for a dual-sided snorkel, as shown and described.
FIG. 1 is a top front isometric view of a dual-sided snorkel.
FIG. 2 is a top plan view thereof.
FIG. 3 is a bottom plan view thereof.
FIG. 4 is a right side elevation view thereof.
FIG. 5 is a left side elevation view thereof.
FIG. 6 is a front elevation view thereof; and,
FIG. 7 is a rear elevation view thereof.
The dash-dash broken lines illustrate portions of the dual-sided snorkel that form no part of the claimed design. The dash-dot-dash broken lines represent the boundaries of the claimed design and form no part thereof.