(Jeremiah Burroughs, "The Incomparable
Excellency and Holiness of God")

"The mouth of the wicked gulps down evil."
  Proverbs 19:28

This is a metaphor taken from the practice of
brute creatures. Take a beast that has been
kept from drink a long time and is exceedingly
thirsty. If you bring it to the water, it will
thrust its head into the water as if it would
devour the whole river and never be satisfied.

That is the meaning of this phrase, "the mouth
of the wicked gulps down evil." When he comes
to his sin, he is as greedy for it as the beast that
has been kept from water is greedy for water.