Comedy is not a science, it's art. Therefore there are no rules and it can be very subjective. What one person finds funny another might cringe at.
One thing worth noting is that when analysing comedy and what is funny, it is almost like it is only visible out of the corner of your eye. As soon as you try and look directly at it and analyse it too much... all of the funniness disappears...
Why do we find things funny? Why does this reaction force us to convulse and make that noise?
I have no idea.
There is no simple answer to why something is funny... Something is funny because it captures a moment, it contains an element of simple truth, it is something that we have always known for eternity and yet are hearing it now out loud for the first time.
I think that our need to feel intelligent comes into play a lot in finding things funny... maybe humour is actually the overwhelming joy at feeling intelligent. Somebody tries to put on their shoes standing up and falls over in the process. They look foolish, we therefore feel intelligent as we are not the one falling over trying to put on shoes.
Someone makes a clever joke and only a few people get it. If we get the joke we recognise the person as being clever and feel clever ourselves as we understood the concept.
So is humour partly to do with self congratualtion at being intelligent?
Comedy is full of opposites and contradictions.