Okla. Stat. tit. 21, § 778

Any person who threatens to publish a libel concerning any other person, or concerning any relative, wife or child or dead relative of such person, or member of his family, shall be liable civilly and criminally to have the same intent as though the publication had been made. But if the threat be not in writing, the threat and character of the libelous matter must be proven by at least two witnesses, or by one witness and corroborating circumstances.