I claim the ornamental design for a flexible rake, as shown and described.
FIG. 1 is a first perspective view of a flexible rake showing my new design;
FIG. 2 is a second perspective view of the same rake;
FIG. 3 is a plan view thereof;
FIG. 4 is a bottom view thereof;
FIG. 5 is a left side view thereof;
FIG. 6 is a right side view thereof;
FIG. 7 is a front elevational view thereof; and,
FIG. 8 is a rear elevational view thereof.
The broken line showing of the rake handle is included for the purpose of illustrating environmental structure and forms no part of the claimed design.