Matthew Henry Commentary Proverbs 10:18-20

"He that hideth hatred is of lying lips; And he that uttereth a slander is a fool. In the multitude of words there wanteth not transgression; But he that refraineth his lips doeth wisely. The tongue of the righteous is [as] choice silver: The heart of the wicked is little worth." — Proverbs 10:18-20 (ASV)

Four things cannot be fully known. The kingdom of nature is full of marvels. The fourth is a mystery of iniquity: the cursed arts by which a vile seducer gains the affections of a female, and the arts which a vile woman uses to conceal her wickedness.