A moderate voltage is more dangerous immediately than a high voltage. This is because a high voltage zap will essentially defibrillate your heart; it stops entirely for a second and begins to beat again. Whereas a moderate voltage won’t stop your heart but can introduce an arrhythmia, which stops it from pumping, leading to very rapid death.
Note: this only applies to very short shocks. High voltage is of course much worse if the exposure is longer, as it quickly fries your tissue.
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