While poking around at this question: Symbolism behind Hepheastus riding a donkey
A common detail in the art struck me, and as a result, I learned a cool new word:
- Ithyphallic: having an erect penis.
So the fellows accompanying Hephaestus are Satyrs, which are almost always depicted ithyphallically, no mystery there. But why (if you'll pardon the mild crudeness) is the mule packing so much wood?
Even when his retinue are portrayed more modestly, the horse's phallus still seems to often be erect and prominent (examples 3, 4 and 5). The first example below is the François Vase, and it portrays many horses, and Hephaestus's is the only one which is ithyphallic, as far as I can tell.
1 - From the François Vase

2 -

3 -

4 -

5 -

It seems like this is a pretty standard element of the depiction of this story. So why is it typical for Hephaestus's mule to have an erect phallus?