1)
What are "Shinav u'Ma'achalos Mesale'osav"?
1.
Rashi: They are outer teeth, knives and inner teeth, respectively.
2)
Why are their teeth like swords?
1.
Malbim (Derech ha'Muskal): Since they do not believe in Divine Torah, Hashgachah, reward and punishment, they have no creed of etiquette. Rather, they are like fish of the sea - the big swallows the small. They eat the poor with their teeth.
2.
Malbim (Derech ha'Pashut): They consume the poor. They are evil to Hashem and to people, in deeds and in Midos. Therefore Hashem punished them!