Weirdly enough, their voices hadn't switched. So what you were hearing was Sans's voice screaming, for the first time since you’ve met him in Snowdin. You were absolutely sure that you were never going to hear a loud Sans or a quiet Papyrus, but hey, what do you know.
http://tvtropes.org/pmwiki/pmwiki.php/Quotes/VoicesAreNotMental
FollowingQuotes / Voices Are Not Mental
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