That's just the reason I DIDN'T tell you. I like to keep the guest appearances in my comic sort of an inside joke to those as webcomic savvy as I. Unless it's something out in the obvious like Ezekiel from Krazy Larry as the Little Blue Man, I want it to be a little bonus for those eagle-eyed enough to notice it. But since you already mentioned it, the first panel of the comic you pointed out is nothing but cameos.
In the second coming of "The Adventures of Captain Mooki" I'm gonna do cameos the same way having the characters I *appropirated* as nonspeaking background characters so I can have deniablility in all copyright incidents that may occur "What Do You Mean That's Jack Skellington?!?! He's Facing the other way, he could just have a giant eyeball for a face! Yeah, that's the ticket!"
P.S. In the spirit of the hidden cameos, I'm also going to be hiding Easter Egg links around the site (One's up already) for you guys to hunt for in the wee hours of the night as you surf the web in hopes of a cure for your insomnia.