This has been true of every dog I've ever known. (Well, at least the ones that I've known well enough to sniff their feet.) When dogs get dirt and dust on the pads of their feet, which then 'bakes in' through perspiration, the resulting smell is not unlike that of a bag of Fritos. In fact, I would venture to say that it smells exactly like a bag of Fritos. (My wife, who's sense of smell is much more discerning than mine, says that sometimes Polly's feet smell more like cheesecorn. I'll take her word for it.) I don't know if this fact makes me like dogs more, or dislike Fritos more.