watch this part: watch what L (the tired-looking guy) says after Misa (the pretty girl) says she wont eat her cake
http://www.youtube.com/watch?v=vx3n1C8KY18&feature=PlayList&p=5895C048D2073337&playnext=1&playnext_from=PL&index=1
it says:
Misa: Man, this has got to be the lamest date i've ever been on.
L: No, no, plz pretend that im not even here, okay? By the way, are you gonna eat that piece of cake?
Misa: Cake makes you fat. Im not gonna eat any.
L: Actually, I found that you don't gain any weight as long as you burn calories by using your brain
Misa: Oh, so now you're calling me stupid? Fine then, ill give you that piece of cake as long as you agree to leave me and Light (the brown-haired guy) alone.
L: Even if i leave you two alone, they'll still be watching on surveillance cameras so it wouldn't make any difference.
Misa: You pervert. Can you stop it with your creepy hobby.
L: Yeah, you can all me whatever you want. Last time for cake.
Misa: Okay, then. I'll just close the curtains and turn off the lights.
L: We have infrared cameras here.
Misa: umm.