Ah man, I got into this same debate with a professor I turned a paper in to a while back.
Technically speaking,
either is accurate. But in the academic world something like "Sniggles'" would
usually mean a plural possessive rather than a singular possessive, so multiple Sniggles owning something/s; that's how it's traditionally been used, anyway. A separated "'s" always denotes a singular possessive and is still fine to use with words that end in "s", so usually that's used for singular posessive rather than "s'" (in my field, anyway), so as to avoid confusion.
So we're both right, and I just like doing it the way that looks weird.