[Papyrus makes a faintly disappointed sound, because - while he wouldn't know Scooby Doo to know the reference - it's the kind of trickery that could work somewhat effectively, with magic to back it. But oil or paint on the face would probably have as good of odds, if they're guessing right about how the mannequins sense things, and splashing them could serve the purposes of tripping and blinding hazard at once.

He's starting to like this idea when the question comes up, and he startles like he's been caught out.]

L-Like this?

[Not nearly as loud as last time, but louder than he's trying to be, so he rushes to half-cover his mouth to better muffle the sound before continuing. If he exaggerates the way he does so, buying for time as he uses the idea of danger to deflect attention, or if there's something conflicted and careful in his face now... Well, there's a lot going on, and there could be any number of reasons for that.]

You mean, uh... Trapped in a shopping center... unbreakable windows, besieged by silent, violent mannequins? No, that's... new. [Mostly.]