When Grim reboots the computer, closely read the on-screen text. About halfway through the loading, you'll see a hidden paragraph: "Did you know that Billy & Mandy started off as an online cartoon? No, it's a lie."
When Grim starts reboots the computer while trying to fix the computer, the reboot screen says "did you know that billy and mandy started as an internet cartoon?... ...it didn't. that's a lie." It also says "matrix okay. sequels not so good."
Greg Eagles said that it is his favorite Billy & Mandy segment.