They have sharpened their tongues like a serpent; adders' poison is under their lips. Selah.
They have sharpened their tongues like a serpent - not that a serpent sharpens its tongue: the point of comparison is to the venom of a serpent. So the next clause, "adders' poison," etc.: cf. David's Psalms 58:4. They have sharpened their tongues to give as deadly a wound as a serpent gives. So David's Psalms 64:3.
Adders' poison is under their lips. Selah - rather, 'asps.' The Hebrew term, `akshuwb (H5919), occurs only here. "Under their lips," cf. Psalms 10:7.