You shine your flashlight at and around your double. It mirrors your actions, and while both lights are not visible in the sunlight you are temporarily blinded as your double hits you directly in the eyes with its flashlight, just as you point yours at its face. After a couple of minutes of this, you put your flashlight away. You can attempt to talk to your double, attempt to paddle around your double, continue paddling straight ahead, or you can use your whistle.