Understanding humor is the key to understanding people. If you understand why a joke is superior, you can express your approval through measured laughter.
Let's begin our study.
A priest and a rabbi walk into a bar. They should have ducked.
That's funny because when you hear the phrase "walk into a bar," you think the priest and rabbi are walking into a pub or tavern, but it turns out they are walking into a low-hanging bar, probably made of metal because when a metal bar and a human head come into contact, the result is a funny clunk sound. This form of humor is called ad absurdium deus. The "ad" prefix has no known meaning in Greek, "absurdum" is derived from the Celtic words "absur" and "dum," and God only knows what "deus" means.
Great, so that's a funny joke. When someone tells it, you can laugh the appropriate amount. But how can we make it funnier?
A goose and a swan walk into a bar. It remains unclear why they did not duck.
This joke is twice packed with double entendres, making what the French would call a quartois entendre. On the one hand, you have the same funny thing going on with "bar" referring not to a tavern but to a metal pipe likely covered with barbed spikes. Now add to that the humor association among the goose, the swan, and "duck," and you have a delightfully fowl joke. That's called "word play," and it's something that is funny. Also know that it's funny when an animal hits its head against something metal, especially if it causes the animal to wobble or bleed.
Dare we make this joke funnier? We dare.
A mallard walks into a bar. Duck!
Some humor strikes the senses at such odd angles and with such twisted force that all mental processing of said humor is bypassed, resulting in a gut-level guffaw. This joke does exactly that.