Jesus uses this as a metaphor meaning the Pharisees will complete the wicked behavior that their forefathers started when they killed the prophets. AT: "You also finish the sins your ancestors began" (See: [[rc://en/ta/man/translate/figs-metaphor]])
Serpents and vipers are the same thing. They are dangerous and often symbols of evil. AT: "You are as evil as dangerous and poisonous snakes" (See: [[rc://en/ta/man/translate/figs-doublet]] and [[rc://en/ta/man/translate/figs-metaphor]])