The Energon Pub

So, I just got Thundershred in the mail. And I'm curious about this slot on his... uh... butt region. Nothing tabs in there for robot mode, or for insect mode. I don't think any of his weapons can fit in there, and it would look ridiculous if they did. Does this slot serve any purpose at all?

Besides the obvious anatomical needs?

Just got mine. I also kind find any good reason for it.