What does Cast doubt on mean?

Cast doubt on meaning in Idioms Dictionary

If you make other people not sure about a matter, then you have cast doubt on it.

Sentence Examples with the word Cast doubt on

Zukal has considered that the lichen acids protect the lichen from the attacks of animals; the experiments of Zopf, however, have cast doubt on this; certainly lichens containing very bitter acids are eaten by mites though some of the acids appear to be poisonous to frogs.

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