Join clips?

In iMovie there is a handy feature called Split Clip, which is useful if you want to use a bit of video in two places or if you want to re-record a line of narration at the point where you muffed it without having to re-record the whole thing.

I also noticed there is a Join Clips command under the Modify menu that is grayed out. I have some narration that I recorded in sections and they would be easier to work with, now that I have them the way I want them, to join them together,. However, when I select them , the Join Clips command is not active.

I looked in iMovie Help and could find nothing about this.