This game tends to feel so buggy. I'm not sure if it's me, or the game, but it skips every so often, it has -REALLY- bad sensitivity, and I die when I never even hit anything.
As to what 'SpinelessCoward' said, Dave is either a ghost, or a figment of imagination. It's kind of like a Sub-Story, a type of story where it's the hidden things that the developers just leave it up to you to figure out and find out for yourself. I'm thinking that there's going to be a deep secret about the school, maybe revealed in the part two? As for the evidence, SpinelessCoward already took care of that.
Uhm. This USED to have badges, but they never worked because it had no Kong API. Rate this up so people know. Or just rate it down if you want people to keep asking for badges...
 "Vector Stunt"){kind=icon}
 "Level Up!"){kind=icon}
 "Accelerator"){kind=icon}
 "Synapsis 2"){kind=icon}
 "Villainous"){kind=icon}
 "Wasted Youth, Part 1"){kind=icon}
 "Splitter 2"){kind=icon}
 "The Undead Survival Test"){kind=icon}
 "Interactive clown tutorial"){kind=icon}
 "Swords & Potions"){kind=icon}
 "Protector"){kind=icon}
 "Easy RPG"){kind=icon}
 "Stay Dead"){kind=icon}
 "The Sagittarian 2"){kind=icon}
 "Epileptic Headsmashing Game 2000+ Deluxe!"){kind=icon}
 "Meat Boy"){kind=icon}
 "Cardian"){kind=icon}
 "Poltergifts"){kind=icon}
 "Destroy All Zombies III"){kind=icon}
You can change the sensitivity in the options screen, and you can turn off the image effects which has been known to fix lag in some cases :)