Where TortoiseSVN name came from?

I has just been asked that this question. And I haven't really known the answer. One supposition that made me smile "Is it because of it is very slow?"
Ok, I suspected the answer is...
The name of the program was fixed when we started, because the CVS counterpart is called TortoiseCVS.
But I don't really see where TortoiseCVS came from? As Wiki says:
The name is a pun on the word shell
Which doesn't make a lot of sense for me. So what's the truth?