Musar к Шмот 11:7

He also diminishes his stature as a human being thereby [(by speaking lashon hara)] until he emerges "worse than a dog," as Chazal have said (Pesachim 118a): "One who speaks lashon hara … deserves to be thrown to the dogs, it being written (Shemoth 23:1): 'You shall not receive a false report,' which is read as you shall not spread, which is preceded by (Ibid. 22:30): '…to the dog shall you throw it.'" The rationale is obvious, as written by the Maharal of Prague: "For the dogs guarded themselves when necessary, from 'sharpening their tongues,' as it is written (Ibid. 11;7): 'And against all the children of Israel, a dog shall not sharpen its tongue' — and he [(a human being)], whom the L-rd accorded understanding and knowledge could not restrain his yetzer from this [(lashon hara)] — wherefore he is 'worse' than a dog."

He also brings himself to eminence in this world, as it is written in Mechilta, Parshath Mishpatim on Shemoth 32:30: "And flesh torn in the field you shall not eat. To the dog shall you throw it" — to teach us that the Holy One Blessed be He does not withhold reward from any creature, as it is written (Shemoth 11:17): "And to all the children of Israel a dog will not sharpen its tongue." Now is this not a kal vachomer [i.e., Does it not follow a fortiori]: If it is so [i.e., that He does not withhold reward] from an animal, how much more so from a human being!

The Maharal of Prague gives another reason. The dogs guarded themselves when necessary [at the exodus] from barking, as it is written (Ibid. 11;7): "And against all the children of Israel a dog will not sharpen its tongue." Yet he [man] whom the L-rd has accorded understanding and knowledge cannot keep his yetzer from doing so — wherefore he is worse than they!