That's because he forgot it was in his pocket. Dave's forgetfulness still is an amazing thing apparently.

He stops running, as soon as he hears Terezi's voice call him though. He recognizes her voice and he looks over, spotting her. "Sup Pyrope. Where you been? I mean, more crappy zombies and giant animals for me, but shit was getting kind of dull. Listening to myself talk is hardly as interesting unless someone else is listening to me too." You better just tell him to shut up, because he's seriously going to keep rambling. "Did you know that slicing through spiders and ants is ten times more gross then just stepping on them? I mean, seriously, that shit is so nasty. Not in the sicnasty way. Just nasty."