The ornamental design for an earplug, as shown and described.
1. Ear plug
1.1 : Perspective
1.2 : Front
1.3 : Left
1.4 : Back
1.5 : Right
1.6 : Top
1.7 : Bottom
1.8 : Perspective
The design shows an ear plug for use in water sports, such as surfing; the ear plug has an body with an upper part and a lower part; a tip is arranged around the lower part that is adapted to be inserted into the ear canal; a membrane is arranged at the front of the upper part, which allows sound to enter the ear plug but blocks water and wind from entering the ear plug.