Charles H. Spurgeon on Psalms 140:3

They have sharpened their tongues like a serpent. To sharpen or whet the tongue imports the keenest and most extreme kind of talkativeness, much more to sharpen the tongue "like a serpent." Naturalists tell us that no living creature stirs his tongue so swiftly as a serpent, and serpents are therefore said to have a treble tongue, because, moving their tongue so fast, they seem to have three tongues. The Psalmist means —the wicked speak thick and threefold, they sting and poison me with their tongues. —Joseph Caryl.