Most of them probably use clever wordplay. Characters might say things that have double meanings, which add to the humor. For instance, a line like 'I'm not lost, I'm just exploring the wrong way' can be both silly and thought - provoking.
They are likely to be full of unexpected twists. For example, a character who seems to be in a very serious situation suddenly finds themselves in a ridiculous one.
The stories in 'best classic humor 72 stories' may often rely on the absurdity of human behavior. People do things that are completely illogical, like building a house out of toothpicks when they have all the materials for a proper one right next to them. This kind of behavior creates a lot of humorous situations as we can all relate to the irrational things we sometimes do.