The inward being represents people's thoughts and desires. AT: "their thoughts and desires are wicked" (See: [[rc://en/ta/man/translate/figs-metonymy]])
Their throat is spoken of as if it were an open tomb, ready for dead bodies to put into it. Possible meanings are 1) "they say that they will kill people" or 2) "What they say kills people" (See: [[rc://en/ta/man/translate/figs-metaphor]])
# they flatter with their tongue
"they say nice things about people without really meaning it"
# their tongue
The tongue represents what people say. (See: [[rc://en/ta/man/translate/figs-metonymy]])
# may their schemes be their downfall
"may their schemes cause them to experience disasters" or "may they become less important because of their schemes"
This is something that causes a person to experience disasters or to lose power. Experiencing disaster or becoming less important is spoken of as falling. (See: [[rc://en/ta/man/translate/figs-metaphor]])