Alder's razor

When you cut a creature that can speak with this razor, they take 1 point of damage. For the next minute, the creature can only utter sentences that can be verified by nonmagical means, such as experiments or observation, or by magical means like Identify or Scrying. Every time the creature is cut with the razor while they are already under its effect, the duration is extended by another minute and the creature takes an additional point of damage. The creature experiences the razor's effect as being at a loss for words when they are trying to say something unverifiable, while verifiable utterances can be spoken as normal. The creature must make an intelligence saving throw. If they succeed, they are able to deduce that they cannot say anything that is unverifiable, but if they fail, they are unaware of this and they don't know why they suddenly struggle to form certain sentences. However, all but the simplest creatures will realize that the effect was caused by the razor.