At the end of a week, God told Moses to go back to Pharaoh with the same demands, and that when he refused (which God would make sure of) to threaten him with a plague of frogs.
So the brothers went back, Pharaoh refused, and then, between the brothers and the court magicians, Egypt was overran by frogs. I mean there were frogs everywhere–in the chamber-pots, the soup tureens, Pharaoh’s wine cup. You couldn’t step without squishing a frog.
After a few days, Pharaoh had a enough of the frogs, so he called Moses and Aaron to him and was all, I’ll let the Hebrews go on that camping trip if you guys get rid of the frogs for me. Moses said they’d be gone by morning, and lo, in the night all the frogs died. So now there were piles of dead, rotting frogs to go with the rotting fish from the week before. When Moses and Aaron came to Pharaoh to set dates for the trip, Pharaoh was all, what vacation? Y’all need to get out there and start sweeping up dead amphibians.
By this point, God was really getting Its smite on. It told Aaron to strike the ground with the magic staff and lo, clouds of gnats arose and began stinging man and beast alike. The magicians tried to repeat the trick, but couldn’t, much to the relief of the Egyptians. They told Pharaoh that the gnats must come from God, since they couldn’t make gnats too.
Then God told Moses to go ask Pharaoh to let the Hebrews go again, or next would come flies. Moses started groaning and caviling at this new torment, so God was all, don’t worry, the flies won’t go into Goshen. So Moses did what God said, and after a few days of gnats and flies, Pharaoh again called Moses and Aaron to him, and was all, ok, ok, you win guys. Make the flies go away, and I’ll send out a notice that Hebrew sacrifices will be permitted in Goshen. But Moses was all, no dice, Pharaoh. Not only will Egyptians stone us if they see us doing our rituals, but also we need to be out in the desert to do them properly. Pharaoh was all, Ra have mercy! Fine, go camping, just don’t go too far away ok? And don’t forget about the flies. Moses was all, I’ll get rid of the flies, but you better not double-cross us again. Pharaoh was all, who me? Never!
So Moses got God to kill all the flies, then of course Pharaoh double-crossed them and forbade the camping trip. I mean, who else but the Hebrews were going to clean up the heaps of dead flies?