Q: How many musicians does it take to change a lightbulb?
A: A-one, a-two, a-one, two, three, four!

Explanation: There are many, many jokes that start ask, “How many ________ does it take to change a lightbulb?  You can do a search of “lightbulb jokes” and see more.  Most lightbulb jokes make fun of someone.  By the way, when I search, I see both light bulb (two words) and lightbulb (one compound word).  When I looked for which is correct, I found this.

This joke is funny because, well, lightbulb jokes are funny.  This one in particular is funny because many musicians start off their songs with the 1, 2, 3, 4 count.

Here is a song that starts with a 1, 2, 3, 4 count to begin.  If you are patient, you will hear it–

Q.E.P.D./R.I.P. Chris