Shmos 4:3 When Hashem has Moshe throw his staff down, it turns into a Nachash. Here Aharon throws down his own staff and it turns into a Tanin. At the river, Moshe is told take the staff that originally was turned into a nachash on the mountain (his own staff) and warn Par'o.

Then in sentence 19, Hashem tells Moshe to tell Aharon to take his staff and stretch his hand out over the "waters of Egypt".

It seems that the point is that it does not matter which staff is being used as it is not a matter of a wizard using an object of power (which might be what the Egyptians thought) but Hashem causing the result.

Update:

I see that you also ask about the difference in usage between nachash and tanin.

The meforshim of the mountain miracles (such as Ramban) connect the snake and the tzora'as to the "loshon Hara" of Moshe saying "they won't believe me". 

The tanin was considered the symbol of Egypt as shown in Yechezkel 29:3 (haftara of Va'Eira). Thus, what was being shown to Par'o and the court was the symbol of Egypt being under the control of Hashem.

Did Aaron's staff turned into a snake or a crocodile?
This is my first post here and I have a question about a CMOS circuit I have been designing for I while using the 4066 (I'm a noob to digital electronics). I am using a 4066 to pass random pulses I generated by feeding a noise generator with two two outputs (the generator is connected to a JFET amp and then clamped with diodes to two different dc voltages) into a 4050 (one buffer for each noise gen output). The pulses work perfectly. The only problem is, when the 4066 is not enabled, about 1 volt of the pulses pass through each switch. I was wondering if there was any way to fix that! Here is my circuit:


