OT: What's in a USB cable?

[John Teller]

USB cable by itself is a nice low-capacitance shielded cable - it's 
ideal for audio and low-signal use.  However, like Mike said, that 
doesn't prevent it from picking up stray signals when one end is left 
unconnected.  Despite the shielding, the cable is subject to the 
triboelectric effect and can actually produce enough voltage to drive 
the USB receiver.  You can see this if you connect one of the twisted 
pairs to the input of a scope and then flex the cable.