A treacherous person can be described as a WEASEL, RAT, RENEGADE, VIPER, SNAKE, or SNAKE in the grass. Weasels are small mammals known for their cunning and sly behavior. Rats are rodents that are often seen as pests due to their destructive habits. Renegades are people who have abandoned their loyalties and gone against the accepted norms of society. Vipers are venomous snakes that are known for their aggressive behavior. Snakes are reptiles that are often associated with danger and deceit. Finally, the phrase 'SNAKE in the grass' is used to describe someone who is untrustworthy and sneaky.