First God taught Moses the old rod to snake trick.
And Moses answered and said, But, behold, they will not believe me, nor hearken unto my voice: for they will say, The LORD hath not appeared unto thee.Then he showed Moses how to turn the snake back into a rod.
And the LORD said unto him, What is that in thine hand? And he said, A rod.
And he said, Cast it on the ground. And he cast it on the ground, and it became a serpent; and Moses fled from before it. Exodus 4:1-3
And the LORD said unto Moses, Put forth thine hand, and take it by the tail. And he put forth his hand, and caught it, and it became a rod in his hand: That they may believe that the LORD God of their fathers, the God of Abraham, the God of Isaac, and the God of Jacob, hath appeared unto thee. Exodus 4:4-5As a final trick (in case Pharoah wasn't sufficiently impressed by the first two), God showed Moses how to make his hand "as leprous as snow" and then change it back to normal.
God said this one was sure to do the trick, even if the snake/rod one didn't.
And the LORD said furthermore unto him, Put now thine hand into thy bosom. And he put his hand into his bosom: and when he took it out, behold, his hand was leprous as snow.(It turned out that these tricks had mixed results. Pharoah's magicians knew the snake to rod trick and could even turn water into blood. But God finally won the Great Magic Contest by covering the land with lice.)
And he said, Put thine hand into thy bosom again. And he put his hand into his bosom again; and plucked it out of his bosom, and, behold, it was turned again as his other flesh.
And it shall come to pass, if they will not believe thee, neither hearken to the voice of the first sign, that they will believe the voice of the latter sign. Exodus 4:6-8
Later during the Exodus, God told Moses to make a "fiery serpent" out of brass and put it on a pole. Then whoever was bitten by one the fiery serpents that God had created to bite the people (for complaining about the lack of food and water) would be cured of their serpent bites by looking at the magic serpent pole.
And the LORD said unto Moses, Make thee a fiery serpent, and set it upon a pole:and it shall come to pass, that every one that is bitten, when he looketh upon it, shall live. And Moses made a serpent of brass, and put it upon a pole, and it came to pass, that if a serpent had bitten any man, when he beheld the serpent of brass, he lived. Numbers 21:8-9