Board Thread:Off Topic/@comment-26397825-20150712053515/@comment-26397825-20150713233638

Make it like one of those eight colour pens - they're really big to hold all the ink, only it can just have to one colour and the rest of the space is used for the ice dust.

Maybe their semblance could be a mental nudge on the person to make them feel like they should tell the truth without embellishing. Most people would do it, but some people would soldier through and tell embellished stories or lies anyway.