Yikes! ...But critters do get shipped everywhere accidently. I even found (and took home) a gecko (a small lizard) when I worked in a retail store some years back.
I wish a rattlesnake was the scariest thing you could encounter in a US Walmart... http://www.peopleofwalmart.com/photos/
Sometimes, not everything you read is true. I thought I had heard of a prior incident with a rattle snake and Walmart. When looking for it, this is what I found; http://nwahomepage.com/fulltext-news/?nxd_id=235207
Oh god! ...Now you started a stupid word game! Will the madness ever end?!! ...We're a bad influence on you De Orc...a bad, bad influence!!!......Run! Run while you still have a pigeon of integrity left. ...Oh god, now you got me doin' it!!! ...(runs away screaming)... Ahhhhhhhhhhhh!!!!