Having considered what scientists can learn from comedians, now is a good time to give a few guidelines on the place of humour in scientific talks. Here are my opinions on the matter:
1. No separate feedline
The classic joke format consists of a feedline and a punchline. Typically, the feedline invites the audience to make an assumption, which is then shown to be erroneous in the punchline. For example, here’s Jimmy Carr:
Feedline: I can’t forgive the Germans for the way they treated my grandfather during the war …
Punchline: passed over for promotion, time and again.
The punchline is funny because it is unexpected. Jokes made by scientists in talks are often so bad that audiences tend to cringe if they feel a joke coming on. The most effective jokes in talks that I have heard have been ones where the feedline is part of the talk itself. Then the punchline is a complete surprise. A very good example of this was given one of our own. It went something like this:
Feedline: Bayesian probability quantifies our degree of certainty, because we can never be completely certain that a theory is true, or completely certain that something is false …
Punchline: except creationism.
2. Shortest possible punchline
Another reason why the joke above works is that it is two words long. It was over before the audience had time to think: “this guy is trying to make a joke.” Jimmy Carr’s advice worth keeping in mind: what’s the fewest words needed to get to the funny bit?
This is important for two reasons. Firstly, it adds to the surprise. Laughter is an involuntary, spontaneous reaction. Thus, the punchline must be punchy. Secondly, not everyone is going to find the joke funny. If you make those people suffer through your joke, they’re going to resent you for it, and possibly be inattentive or overly critical of the rest of your talk. So make it quick!
3. Don’t pause for laughter
The worst attempt at humour in a scientific talk that I have ever come across came from an astronomer who shall remain nameless. (S)he was from an institute whose acronym is CITA, and was reminiscing about time spent at a particular institute:
“In those days, the institute was called the Institute Of Theoretical Astrophysics, or IoTA. As the research at the institute became broader, it was decided that the name should be changed to the Institute of Astronomy or IoA. We won’t be doing the same thing at CITA … You know (single laugh from the audience) because then it would be … (awkward pause, no more laughter) … you know … (chuckles to self) … the CIA … like the Central Intelligence Agency … the US government agency … which we aren’t … so we didn’t change it … um … anyway …”
It was embarrassing, and annoying. My office mate, a former stand-up comedian himself, described it as “negative comic timing”.
If you pause after your joke, and no one laughs, you’ll look like an idiot. Not only have you wasted your audience’s time with the joke itself, you’ve provided the added bonus of an uncomfortable silence. There is a huge difference between being perceived as someone who is funny and someone who thinks they’re funny. If you just drop the punchline (using the same delivery as the rest of your speech) and then continue on, then you’ll probably get away with a bombed joke. At worst, it will seem like a slightly odd comment, and be immediately forgotten.
Always know what you are going to say after your joke. Don’t wait to see if anyone laughs – just move on. Only pause if you are interrupted by laughter. (And for the love of Thalia, never ever explain the joke.)
So here is my advice to would-be science comedians. If you want to include a joke, don’t let them know it’s coming, don’t let them know its happening, act as if it never happened. Good luck!
More in this series:
Public Speaking for Scientists:
Letters to Nature 
Re: “except Creationism”
A particularly good example, because it won’t offend anybody – regardless of which side of that particular fence you’re on, you’ll agree!