List weirdness - what the heck is going on here?

[Rotwang]

Hi all, I've been trying to make a class with which to manipulate sound 
data, and have run into some behaviour I don't understand which I hope 
somebody here can explain. The class has an attribute called data, which 
is a list with two elements, one for each audio channel, each of which 
is a list containing the audio data for that channel. It also has 
various methods to write data such as sine waves and so on, and a method 
to insert data from one sound at the start of data from another. 
Schematically, the relevant bits look like this:

class sound:
     def f(self):
         self.data = [[0]]*2

     def insert(self, other):
         for c in xrange(2):
             self.data[c][0:0] = other.data[c]

However, the insert method doesn't work properly; x.insert(y) adds two 
copies of y's data to the start of x's data, instead of one. From a 
session in IDLE:

 >>> x = sound()
 >>> y = sound()
 >>> x.f()
 >>> y.f()
 >>> x.data
[[0], [0]]
 >>> x.insert(y)
 >>> x.data
[[0, 0, 0], [0, 0, 0]]

But suppose I replace the line

   self.data = [[0]]*2

with

   self.data = [[0] for c in xrange(2)]

Then it works fine:

 >>> x = sound()
 >>> y = sound()
 >>> x.f()
 >>> y.f()
 >>> x.data
[[0], [0]]
 >>> x.insert(y)
 >>> x.data
[[0, 0], [0, 0]]

Can anybody tell me what's going on?