Some advice from an article in Lawyers Weekly:
If the witness has to answer “yes” to anything during cross-examination, “make sure it is a very proud ‘yes,’ rather than looking like a deer in headlights when you’re cross-examined. That way the jury won’t think the opposing lawyer is scoring any points.”
If the police come in my office and arrest me for murder as I’m typing this post, I’m convinced I would have a guilty look on my face as they hauled me out of here. The same holds true with many witnesses: they have the “You got me on that one” look on their faces even when asked a question like, “Your social security number is 123-45-6789, isn’t it?”
The take home message is that if you have a client like this when you are preparing for cross examination – and you are only going to be able to know if you do a live cross – it makes sense to remind the witness not to answer as if the defense lawyer has just scored a big point. But there is one caveat: some people just can’t help it.