Here's what happens when a jury is deadlocked

After four days of deliberating, jurors in Bill Cosby's trial said they are deadlocked and cannot come to a unanimous decision on any of the three charges against the comedian.

So now what?

First, Judge Steven O'Neill sent them back into deliberations in another attempt to reach a verdict, which must be unanimous. Cosby, 79, has pleaded not guilty to three charges of aggravated indecent assault.

In court Thursday, O'Neill read to jurors what is commonly known as the Allen Charge, or the "dynamite charge," which is a set of instructions that asks jurors to re-examine their own views and opinions in order to reach a decision. It's called the Spencer Charge in Pennsylvania, according to Jim Koval, director of communications for the Pennsylvania Courts.

"I am required to read you an instruction. The jury foreman has informed me that you are deadlocked," O'Neill said. "If you are still deadlocked you should report that to me. If you've reached a unanimous decision on some of the charges, please report that back to me."

The 12-person jury is made up of four white women, six white men, one black woman and one black man. They were bused in from Allegheny County near Pittsburgh and have been sequestered for the trial.

There is no rule on how many times O'Neill can order jurors back to work under the Spencer Charge.

The announcement of a "hung jury," as it's known, leaves the possibility that O'Neill will declare a mistrial. In that case, Cosby would not be found guilty, nor would he be acquitted. Following the declaration of a mistrial, prosecutors may choose to retry the case with a different set of jurors, or they may cut their losses.

Prosecutors say Cosby drugged and sexually assaulted Andrea Constand, a former Temple University employee, at his Pennsylvania home in January 2004. The case has little forensic evidence, and legal experts have said it fits the "he said-she said" dynamic so common to sexual offense cases.

The trial began on June 5, and the jury began deliberating Monday evening. After 31 hours of deliberations, jurors said they were deadlocked.