I'm All Out of Funny Tonight

I've got a strange sense of humour, I'll be the first to admit that.  One of the things that I enjoy are jokes/puns that have a second meaning (no matter how obscure) that the originator was unaware of.  See, for example, the following picture:

Now, the obvious answer is "UR", or "you are".  I walked by it for days, and it didn't really register just what the letters were, until a couple of weeks ago.  "U and R," my brain went, "U and R.  U R.  Ur.  Wasn't there something else that was called Ur?"

Now, the obvious things for my brain to associate with Ur would be the ancient city or the prehistoric continent.  That, however, wasn't what was rattling in my mind.  What was rattling in my mind was that it had something to do with something religious, so today I went and looked for what it was.

In Mandaeanism (a pagan Gnostic sect, and the only surviving Gnostic sect), Ur is the son of Ruha (a "wicked spirit", and one of the creators of Adam).  He is "The great serpent. The dragon that devours bad souls. Rebellious."

The Catholic Encyclopedia (never the best source for these things) describes him as "the prince of devils," and the 1911 Encyclopedia Britannica describes him as "the personified fire of hell" and goes on to note that:

"In anger and pride [Ur] made a violent onset on the world of light, but was mastered by Hibil and thrown in chains down to the "black water," and imprisoned within seven iron and seven golden walls. By Ur, Ruha, while P'tahil was engaged in his work of creation, became mother of three sets of seven, twelve and five sons respectively; all were translated by P'tahil to the heavenly firmament, the first group forming the planets and the next the signs of the zodiac, while the third is as yet undetermined.

"At the end of the world the devil Ur will swallow up the earth and the other intermediate higher worlds, and thereupon will burst and fall into the abyss of darkness where, along with all the worlds and powers of darkness, he will ultimately cease to be, so that thenceforward the universe will consist of but one ever-lasting world of light."

For further explanation: P'tahil is an agent of the World of Dark, sometimes identified with the demiurge; he (along with Ruha, depending on what source you use) created the majority of the physical world, but bungled the process of doing so, requiring the intervention of Hibil, an agent of the rival World of Light, in order to fix things.  At least, I hope I got all that right; what information there is ranges from obviously biased (Catholic Encyclopedia) to conflicting (just about everything else).

So, what's missing in their ch--ch?  The answer is: the great serpent and devourer of worlds.  Yeah, I know, I get amusement out of the strangest of things.