I wasn't sure what I'd find in this thread - not least since I was discussing the cuddly/sinister borderline yesterday with regard to tribbles.
(For those who don't know, tribbles are small, furry, adorable creatures in Star Trek who eat a lot and reproduce stupidly fast. So far so cute. However, they look similar to (which is to say both are just balls of fluff) wig-wigs from the Edge Chronicles, which are more or less the same but the whole thing opens up and is just full of very very sharp teeth).