The ones I co2 myself he ate so I don't think its the co2 unless the breeder I bought the others from used way to much. As for the smell of them it could possibly be a chemical smell. I'll have to thaw and really smell and try to identify it. It didn't smell like ammonia to me. But there is definitely a noticeable strong smell coming from them. I also think its strange that both the smalls and mediums I bought were like that. Idk if the breeder I bought from freezes a bunch and sells them until there gone or freezes them when someone calls and places an order. They were packaged in gallon bags, smalls all in 1 bag and mediums in another. I had to vacuum seal them myself. I noticed some had bedding stuck to them. Maybe his rat cages are really dirty and the rats have been in there own feces and urine and that's the smell I'm noticing. I didn't see the rat operation so I can't say that there dirty. Good thing it only cost me $25 for 28 rats.