Exodus 7

And God said to Moses, "See? Now I’ve made you like a God to Pharaoh! And Aaron is your prophet!" So, just like the whole God-Moses relationship, where God told Moses what to say, Moses told the Israelites, and they all ignored him; likewise, Moses would tell Aaron what to say, Aaron would tell Pharaoh, and Pharaoh would ignore him. A time-tested, proven system.

Of course, God wasn’t just putting Moses through this because it was funny. That was just a bonus. God’s real purpose was to give himself the opportunity to show off in front of the Egyptians, so they would all start worshiping him instead of all those other gods they liked so much. God figured that if he just stalled things long enough to plague a bunch of Egyptians, followed by Pharaoh releasing the Israelites, the Egyptians would be so impressed that they would fall down and worship him and, if all went according to plan, eventually start in with the tithing.

At any rate, after telling Moses the grand master plan, he sent him and Aaron off to go do the snake trick for Pharaoh. Moses told Aaron to turn his staff into a snake, which he did. Pharaoh, unimpressed, called in various magicians and sorcerers and whatnot and told them to duplicate the trick. With little trouble, they all turned their own staffs into snakes, which Aaron’s snake promptly ate. Pissed off that Aaron’s gluttonous snake had just eaten a bunch of perfectly good staffs (temporarily turned into snakes), Pharaoh refused to let the Israelites go.

God told Moses to tell Aaron to go out to the river in the morning and wait for Pharaoh to show up, and stretch the snake-staff over the water and turn the whole river into blood. Aaron did this, and all the water in the river turned to blood, and all the fish died, and the whole place stunk like hell. Pharaoh, between fish-stench-induced dry heaves, told his magicians to duplicate the trick, and they did so. Suitably convinced that the whole river-to-blood thing was just a silly parlor trick, Pharaoh went back into his house to have grapes fed to him by one of his many mistresses, or whatever it was he did in his spare time. Meanwhile, the Egyptians started digging around desperately looking for water that hadn’t turned into blood before they all died of thirst.

A week passed after the whole bloody river incident, and the story continued in the next chapter.