If you refer to a word or phrase you mentioned earlier in your presentation, that's a callback. It works well if the previous piece of material got a good laugh, or if it was a groaner. If the previous material was good, mentioning it again will get more laughter and will make you look polished for being able to tie the previous material to the present material. If the previous material was poor, the callback will show your willingness to tease yourself, which is an admirable quality the audience appreciates.
Here's how it works: Let's say you used a successful two-liner in your presentation Don't rely on health books too much. You could die of a misprint. Later in your presentation someone might notice a misspelling in one of your handouts or visuals. You could then "call back" and say, "See, that's one of those misprints I was telling you about earlier."
Another thing that might happen, that is just as good, is that one or more of the audience members might make the connection and do the callback for you. One of them may blurt out something about your health book line. That's great if they do. You are getting them involved and allowing them to feel superior to you, which makes them the stars. You could then comeback with, "See, I put that there to test you." When you really get confident, you might actually make the misprint on purpose to set up this whole scenario.
