Why does it say "Shanenu Leshonam"?
Radak: This is like "Chetz Shanun" (Mishlei 25:18). They sharpened their tongues like a snake that sharpens its tongue when it comes to bite.
Malbim: This refers to pursuers who seek to harm without any personal benefit (refer to 140:2:2:2). Their tongue is like a snake, which does not bite for its benefit, rather, due to its evil nature. Its bite is with the tongue, which is more internal than the lips. So they speak Leshon ha'Ra covertly, without benefit.
What is "Chamas Achshuv"?
Rashi: Chamas is an expression of venom, like "Chamas Taninim Yeinam" (Devarim 32:33). You cannot explain it to mean anger, for it does not apply to wine! Here it is venom under the lip. Achshuv is Akavish (spider).
Radak: Chamas is venom. Achshuv is a kind of snake. It is very harsh and evil.
Malbim: This refers to pursuers who seek to harm for their benefit. An Achshuv (tarantula), its anger is revealed under the lips, which are more external than the tongue. So they fight wars openly, for their benefit (extortion) like a tarantula bites for its benefit, to suck man's blood.
Why does it say "Tachas Sefaseimo"?
Radak: When an evil person is angry and speaks in anger, fluid exudes from his mouth and goes under his lip. It is compared to venom that a snake casts.
