We have a bantam frizzle cochin who is now smelling strange. It's a bitter, sort of sour smell, and it seems to be coming from all over him, not his vent area. He seems normal otherwise -- eating, drinking, pooping, no drainage or eye issues, no sneezing. We have smelled this odor before when we go to a particular auction in our area, but don't know what it is. He's the only chicken in our flock who has this smell. Any idea what causes this sort of "sick" smell? Thanks!