Need Advice. Goat Down with backend problems??

[Charlie Horse]

What. Thats sure sad and random. Normally I have ideas about what something could be, but this makes little sense. Its like if your car's AC came on when you adjusted the rear view mirror.... I dont know where to start. If it was an infection in the spine or something it'd do more than one leg. If it was a wound, you wouldnt think it'd be fatal like that. Best guess it'd have to be a virus of some kind, or a snake bite?