It's a delicate art, really. You want to convey a message, but not so much that you actually convey it. A well-placed tongue-biting is an exercise in subtlety, like a delicate dance with a sharp object.
But be warned, there are risks involved. If you're not careful, you may end up with a mouthful of metal.
So, if you're feeling tongue-tied, just remember: it's not just about the words, it's about the holding your breath you're holding.
Or, if you're feeling really tongue-tied, just pretend to be interested.