What is a “dynamite charge?”
Apparently this is the “dynamite charge:”
Here is the definition of an Allen charge:
http://www.lectlaw.com/def/a105.htm
In short: “Jury, your duty is to reach a verdict. A lot of time and money has been spent on this trial, with a lot of effort put into presenting the evidence to you. No one could be better judges of whether the defendant is guilty or not than you and there’s no reason to expect another jury to be better and smarter and more dedicated than you. If you can’t all agree that the evidence shows guilt beyond a reasonable doubt, then you should reach a verdict of Not Guilty.”
The etymological origin, I believe, is to breaking up a logjam.