The video embedded below gives advice on how to testify in court. I must admit that it struck me at first as a joke. But, the advice given in the audio track is sound. And that witness sure did clean up pretty nicely!
I think that this video can be useful in introducing students to the idea that HOW a witness testifes is as important, if not more so, than WHAT the witness says. And also to the concept that witnesses can and should be prepared to give their testimony.