Inexplicable Screaming

Here's a picture of Janey outside.  She is completely happy, having a wonderful time.  We are all playing with a remote control toy in the glorious fall afternoon.

Here is Janey literally seconds later.  She is screaming, as loudly as it's possible to scream, the scream that anyone hearing would be forgiven in thinking is the scream of someone badly hurt.

What happened in between?  Nothing.  Nothing at all.  I challenge even the most devoted believer in behaviorism to figure that scream out.  It had no trigger.  No external trigger, anyway.

What happens?  Does Janey remember something that upsets her?  Does she picture some way things might go very wrong?  Does she just feel like screaming?

This scream, this scream I don't even think you can picture unless you've heard it, keeps us from doing so much.  We had to come inside when she started screaming.  We have no choice.  We have to leave a store if she screams there, leave a restaurant, leave anyplace.  And lest that seem like the reason for her screaming, often, as soon as we leave, she screams again.  There is no pattern we can figure out.

Now, a short time later, Janey is perfectly happy.  She moves on fast.  We don't.  I want to understand the screaming.  I want to help my sweet girl with whatever makes her so very sad, or angry, or scared.  I would do anything to help her, if only I knew what to do.