In linguistics, comparative illusions (CIs) or Escher sentences are certain comparative sentences which initially seem to be acceptable but upon closer reflection have no well-formed meaning. The typical example sentence used to typify this phenomenon is More people have been to Russia than I have. The effect has also been observed in other languages. Some studies have suggested that, at least in English, the effect is stronger for sentences whose predicate is repeatable. The effect has also been found to be stronger in some cases when there is a plural subject in the second clause.