This is a classic joke from the movie "Monty Python and the Holy Grail"! There's no real answer to the question, as it depends entirely on what kind of swallow and what it's doing.

Here's why it's funny:

* It's nonsensical: The question is absurd, as airspeed is a measure of speed, not a characteristic of a bird.

* It plays on the absurdity of the movie: The movie is full of ridiculous situations and jokes, so this question fits right in.

* It highlights the humor of a seemingly important question: The characters in the movie act as though the question is serious, making the absurdity even funnier.

So, while we can't give you a real answer to the airspeed of a swallow, hopefully this explanation gives you a chuckle!