1. How they kill the animals
Many fast food companies kill their animals mercilessly and in an inhumane way because it cheaper and they simply don't care about the animals.
Here is a link to a PETA site:
2. Who knows what in it
Who knows what there food is made out of. It could be made out of pink slime or radioactive chicken, flavored to taste like chicken since it taste so bad. I try to avid eating at fast food restaurants, occasionally I would just get fires and a drink because I know they can't screw those two things up.