We used to keep our feed in a giant plastic dustbin. One day, when the bin was nearly empty, we noticed a hole gnawed in the lid. Inside was one dead rat and the half-eaten remains of several other rats. Presumably they had chewed their way in, eaten the rest of the feed, then eachother, then the last one got thirsty and died. Now we use metal bins and they definitely can't chew their way into those.