George Zimmerman's murder trial is underway in Sanford, Florida.
The neighborhood watch volunteer is charged with second degree murder in the shooting death of Trayvon Martin.
Zimmerman says he shot the unarmed teen in self defense.
Defense attorney Don West told a knock-knock joke during his opening statement.
"Knock knock. Who's there? George Zimmerman. George Zimmerman who? Good, you're on the jury. Nothing? That's funny after what you folks have been through the last two or three weeks."
A jury of six women will decide Zimmerman's fate.
Watch the video below.