There are people that we expect to espouse robot snakes, but Elon Musk wasn't one of them. Nevertheless, Tesla Motors has released this video of an experimental robot snake charging arm that plugs itself in:
The video comes with no written description, but Wired's got a line on what the robosnake is for. The first reason is that a self-parking car isn't much good if you need to follow it into the garage to plug it in. As for the second reason:
Charging cables soon may be too heavy to lift. Much of the R&D in the EV industry is focused on reducing charging time, most likely by pumping more voltage into the car. That requires a heavier cable.
From a design perspective, the snake form factor seems to be a logical choice: It can move up-and-out-of-the-way, yet can lean forward with enough leverage to plug itself in. It also seems ideal to plug in at different heights (to accommodate what will one day be a range of Tesla vehicle styles). A series of hinged arms might be able to accomplish the same thing, but the robosnake is unquestionably more elegant, if a bit creepy.