Hi Renault8Gordini,
as Crutschow already pointed out direct HV generation is lethal. Here is a circuit which delivers timed "shocks" of 15.5, 24 and 31ms. The equivalent power using an ignition coil is 250, 400 and 450mJ, enough to scare the oppossum away but not deadly.
The dual switch is used for circuit safety. If the switch fails the timer circuit might get stuck with a high output, thus causing the MosFet transistor to conduct continuously and frying the transisistor or the ignition coil, most likely both of them.
Boncuk