… does electricity cause your muscles to do the same thing everytime?
No. I believe that in general, DC usually causes your muscles to jolt once then relax, while AC generally causes your muscles to jolt shut and pretty much stay there. Keep in mind there are exceptions as electricity is inherently unpredictable, but this is what is generally thought when comparing AC to DC.
… does anyone know how many amps it actually takes to kill a person?
I believe the MythBusters use 6 mA through the heart as the threshold of death.
I always hear the "its the amps, not the volts that get you" warning…
Actually, both amps and volts can kill you, but they do it in different ways. Volts kill you by disrupting the brain's involuntary nervous signals to breathing and pulse. In this case, many victims can be resuscitated by starting CPR as soon as possible. Amps, on the other hand, kill you by cooking your body tissues. The internal resistance of the human body causes heat, and CPR doesn't help that much for un-cooking you.