How to take this kind of photo with a canon rebel t3i?

http://bathroomstallfame.tumblr.com/
k i'm not sure if you can see but her profile picture has a little light leak looking thing and i was wondering if anyone knew how to do that on a canon rebel t3i

she said she had a Nikon D90 and I put it on "p" at night and it sounds like the camera is taking two pictures so between clicks move the camera a little and the light will move accordingly

does anyone know how to do this on a canon?!

It's a light trail from a moving light source during a long exposure.

It's not a light leak.

Looks like someone has used slow sync flash. Basically flash combined with a slow shutter speed, at night.

What happens is that the shutter opens when the flash fires, but remains open longer. So if you move the camera while the shutter is still open, any ambient light will be motion blurred.

So put your camera on Manual mode, use the flash, set a slow shutter speed (like 1 second or more) … And you're all set to go. Take your subject somewhere there's little or no light, perhaps only lights in the distance. Fire the shot, then move the camera while the shutter is still open.

BK explained it perfectly.
i do this with my rebel.
using a long shutter speed with flash can make the person appear and the light trail.
i did this once with a glow stick and twirled it around with my face in the middle i looked like a floating head oh i didn't use the flash i used a different light manually just had a friend flash the flash light on my face.
so much fun!