Are they skin-on-skin? If not, then you have a level of electrical insulation that would prevent the shock from going from one person to the next. If a dog has his teeth sunk into the person, then there would be electrical connectivity.
All that voltage works on the nervous system.
If it were enough to transfer to another person, I’d think it would have a more devastating effect than circuit interruption of the CNS.
Taser will only apply current between the two probes. If it’s a 50,000 volt shock, one probe is 25,000 volts positive and the other is 25,000 volts negative. That means it’s 25,000 volts MORE negative than ground, so the current will flow to that probe and not try to go to ground through another path (or person)