Not many non-Germans know how to count in German, so if you didn’t get this joke on the first read, don’t worry – you’re not a lot dumber than the average English native speaker.
But if you feel like upping your game a bit, here’s why it’s funny: the German word for “three” – “Drei” – is pronounced just like the word “dry” in English. Also, “nein” is the German word for “no.” Now, go impress some Germans with that knowledge!
Just Keep Moving. Or Not
The term "inertia" in physics refers to the notion of objects tending to stay in their current situation, i.e., if they're currently still – they'd remain still.
So, if the new theory complies with inertia, it only makes sense for it not to be going anywhere. Or something. For the sake of the joke, we'll ignore the fact that the other part of inertia means that moving objects will aspire to remain in motion.
You'll need an ear (or an eye?) for puns and some world geography knowledge to understand this smart joke, so pay attention: the Seine River runs through Paris, and while it looks breathtakingly beautiful, and can also literally take your breath away if you happen to drown it.
Simply put, jumping off a bridge into this river would be insane! This joke plays on the fact that "in Seine" (i.e., inside the Seine) and "insane" (as in, completely bonkers) sound exactly the same.
You might know the phrase "I think, therefore I am," (because it's super famous, duh) but unless you're a philosophy buff, you probably didn't know it was said by 16th -century French philosopher René Descartes.
When you consider this famous quote by Descartes, you can easily realize why the man instantly disappeared upon admitting that "he thinks not." We think that's pretty darn clever.
Don't Drink and Derive
We're no mathematicians, so here's our explanation for dummies on the meaning of "derive" in math: if we gather correctly, it means doing some kind of calculation to get from one result to another (sorry, that's the best we've got).
So, basically, it is something mathematicians often do; and it also sounds a lot like "drive" – which is definitely something you shouldn't do after drinking. This should explain the joke to you!