Guinea pigs can be very docile and personable. I had one as a kid and I'd take him out and he'd run all over the floor and make little sounds and sit in my lap and shit.
I have a permanent mental image of walking past an old lady in brightly coloured clothing selling roasted guinea pig on a stick in Cusco. They were skinned, impaled, crispy and their faces locked in an endless death scream.
As a side note, I'm thinking elementary school science teachers could use guinea pig fighting to demonstrate the properties of electrons and neutrons to little kids.