Yeah, I looked at the punch line again and I just wasn't feeling it. I'm not much on colon jokes to begin with and despite what Doc might presume, Vexxarr DOESN'T have any external plumbing. So rather than end with the "poop chute" (with deference to Mr. Hanks) I thought I'd go a slightly higher and slightly more esoteric road and let your imaginations go where they may.
I have to imagine that an eye exam might bear a more heightened sense of foreboding for Vexxarr then we might experience. Otherwise, I'm not sure Earth medicine offers him much in the way of fear.