If you have the "anti red-eye" setting on, your digital camera will shoot out a very SHORT burst of flash right before the actual picture taking flash- that non-blinding pre-burst is designed to allow the subject's pupils to contract first, so that by the time the main flash comes on 1/4 second or so later, the subject's pupils have already contracted to some degree. This does two things- 1) it closes those pupils enough to avoid the huge green or red "red-eye" reflection from the back of the open retina, and 2) It is less blinding and uncomfortable to the "flash-ee".
Look to see if your digital camera has a red-eye feature you can just leave on all the time.