Crack.
It sounded like a knuckle cracking. I asked you if you were okay, and you started to cry. Oh, how you cried. I had been on the phone with Auntie Anna throughout this whole incident, and she could hear how upset you were. I hung up with her to calm you down, and you did calm down, but you wouldn't use your right arm at all. If I touched your elbow, or if you shifted your weight onto your right arm, you started to cry.
I started to panic. I called the pediatrician's office, and thankfully, the physcian's assistant agreed to see me on her lunch break. Everyone figured you had nursemaid elbow, otherwise known as a dislocated elbow, which is very common in kids your age. The PA tried four different times to put your elbow back in its place, but she said she actually thought it was already back in place, because she didn't hear the characteristic "click" of it popping back into position. She thought it was perhaps just sore, so she advised me to follow up in a day or two.
I took you home for a nap, but when you woke, you were miserable. All night, you would not use your right arm. It was the same thing when you woke up this morning. So, today, back to the pediatrician's office we went. You got x-rays, and the pediatrician couldn't see anything. So, after a nap, off to the orthopedist we went.
The orthopedist thinks that your elbow did, most likely, get dislocated. You might be having some residual soreness, or you might have a small fracture in your joint that is not visible on the x-rays. He advised that we put you in a cast for a week. The cast will prevent you (or me!) from re-injuring your elbow. It will give your ligament a chance to tighten. It will also give any possible fracture in there a chance to heal.
So far, you don't seem to mind your cast.

Baby Girl, I'm so sorry. I feel so badly that you were injured in my hands, that I caused your injury. I'm afraid the days of that little game are now over. I love you and would never purposely cause you harm. I guess this is just one more good story you can give me grief about in the years to come:
"Hey, Mom? Can I go to the dance? Before you answer, remember the time you ripped my arm out of the socket?"