It takes 30 milli Amps to kill a person.
Just think of a person as a big resistor. The more Voltage you apply the bigger the current that flows through the resistor.
Ie Double the Volts 115 to 230 and double the current.
If don't apply the voltage at either end of the resistor (Wear rubber boots) It don't hurt.
As for 25000 Volts vs Humans If the contact is not enough ie very very big resistor you'll only get a little current.
On a slightly different topic
3 phase. The power delivered is constant that means for a motor it runs smoothly and very little vibration.
1 phase The power pulses at twice the mains frequency. Giving alot of vibration in a motor. You don't usually find a single phase motor bigger than 2 hp