The third sign at the burning bush is the one that rehearses the first plague. Targum Pseudo-Jonathan preserves it with bare clarity: thou shalt take of the water of the river and pour it on the ground, and the water that thou shalt take from the river shall become blood upon the ground.
Notice the precision. The water does not turn to blood in Moses' hand. It does not turn to blood in the jar. It turns to blood only upon the ground. The transformation happens when the Nile water leaves its source. This is not a magic trick; it is a theological argument encoded as a sign.
The Nile as Egyptian God
The Nile was not just a river in ancient Egypt — it was Hapi, a deity. Pharaoh himself was believed to command its flooding. For Moses to carry Nile water out of the river and watch it become blood is to stage, in miniature, the claim that the river's divinity is borrowed — and revocable.
The sages of the Targumic tradition see this sign as the most pointed of the three. The first two (serpent-rod, leprous hand) are about Moses' authority. The third is about Egyptian theology. Every drop of Nile water that turns to blood on dry ground is a quiet argument that the river belongs to the Holy One, not to Pharaoh.
The takeaway: if the first two signs do not convince the Israelites, the third one does double duty. It convinces them — and it previews the undoing of Egypt's most sacred resource. Pharaoh will learn later what the slaves are about to learn now: the Nile has a Maker, and the Maker is listening.