Sarcasm can be hard to detect in writing. But first, the humor:
We’ve all heard of Ivan Pavlov and his dogs, how they learned that food was on the way after a bell rang, and they started salivating before the food showed up. Even if the food didn’t show up! (We call this a conditioned response. It has several other names, too.) Hence the first pun in the comic.
The other one is a little trickier. You have probably heard of the Heisenberg uncertainty principle. It’s the rule that you can’t measure both the location and speed of a subatomic particle at the same time. A key here is that we’re talking about subatomic particles, where any way we try to measure the particle affects it. Makes it twitch, you could say. When you try this with large objects, though, measuring it doesn’t have a material effect, so you can measure both. Shining radar at an airplane, for example, doesn’t make the plane twitch enough to count.
Quantum physics came up with a corollary of the uncertainty principle, that until you measure a particle, it could actually be in more than one state. Edwin Schrodinger thought this was paradoxical, and he made an analogy of the situation by describing a cat in a box with poison and a triggering mechanism and we didn’t know whether it had triggered or not. Thus, he said, quantum physics claims that the cat would be both dead and alive until we look. That’s a lot to say to arrive at this: he was being sarcastic. The cat is a large object, not a subatomic particle, so it is either dead or alive, but not both.
So the comic is funny because it cleverly alludes to two heavy-duty scientific discoveries, but you should still be alert for sarcasm.