When Corday and Greene are in the trauma room after Dr. Cameron leaves the scene, Dr. Corday has put on a blue lead lined vest for the x-ray but it is gone in shots where the camera is behind her.
When the yellow balloon pops in the coffee shop, the sparks from the charge used to explode it are clearly visible.
Mrs. Howard, the woman in the coffee shop who tries to touch Carol's belly, winds up dead after the truck drives into the shop. However, she shows up again in Season 7 as a demented old lady who shoots up the ER during a confused state ("Survival of the Fittest").
When the pickup truck rams the coffee shop, there is a side shot, then a front shot. If you look to the left side of the front shot, the camera and stand they used for the side shot is clearly visible.