Shots Make Me Sad

I took Nate to get his 4 month shots this afternoon. It's one of my most hated experiences of life. There's this moment that is absolutely horrible. The baby is laying there on his back looking up with bright eyes and a happy grin...oblivious to what's about to happen. Then- the needles hit the legs and about 2 seconds later the baby's face changes to a look of utter shock. Then his face reddens as his cry blasts our ears with the sounds of fear and pain. I feel sad because there is no way I can prepare the baby for what is about to happen and no way to explain why it has to happen. I know these shots are for his own good, but I dread them every time. Of course, after only a few minutes things get back to normal, and everybody calms down. It takes much longer than a few minutes for me to erase the image of the baby going from serene to screaming however.