Romeo killed...Benvolio?

I've mentioned before that a friend of mine teaches Romeo and Juliet.  We had dinner this weekend, and I asked her how the class was going.  "Well," she said, "I never knew that Romeo killed Benvolio.  I saw that on a test I was grading today."

I didn't pester her all through dinner since I know she doesn't love to talk about Shakespeare all night.  But it's got me wondering.  I wasn't there.  I don't know what leads up to such an answer.  But why would a student give that answer?  I figure it's pretty unlikely that they've misunderstood the story so much that they think that Benvolio was killed by Romeo.  More than likely they know that Romeo killed somebody (that's probably how the question was asked, who does Romeo kill in Act III), and they blanked on the name.  They then think of all the names they can remember and pick one that sounds right.  That's not necessarily a problem of understanding, that's a problem of recall.  The name Tybalt doesn't stick in the head the same way that Romeo/Benvolio/Mercutio do.  Those three also seem to come as a set, their names all sound similar.  But Tybalt's out in the cold, you have nothing to anchor him to.  I suppose his name sounds a little like Juliet, or Capulet (that trailing T), but obviously not enough.

But how do you fix that?  Say that you're about to teach the class, and you know that at the end of class you're in danger of getting answers like Romeo killed Benvolio.  What do you emphasize while teaching the story to prevent such mistakes from occuring?