It turns out that you can't bring a witness to the stand via Skype for a nationally televised trial like George Zimmerman's without dozens of trolls calling in to talk with that witness!
The witness, Scott Pleasants, is a professor at Seminole State College in Florida, and was formerly Zimmerman's teacher; his testimony's not particularly important, it seems, but his inability to make the 15-minute drive from the college to the Seminole County Courthouse in Sanford and the prosecution's inability to go full-screen with the call and/or turn off contact from people beyond the account's contact list made this moment happen. The name of the account being used to connect with Pleasants was fairly clear to anyone who could squint, and there is, of course, a thread on 4chan's /b/ board dedicated to calling in.
After the notifications for multiple incoming calls covered up Pleasants' face, the court chose to switch his mode of testimony to a phone call, which resulted in a lawyer leaning up against the witness stand and talking into a phone set up next to a microphone.
Headline News anchor T.J. Holmes summed the fiasco up pretty well: "Okay. That didn't work."