When you are quite defenceless it really helps to mimic something else, and as seen below there are a number of caterpillars in Hong Kong that look a lot like snakes.
Picture above of the Common rippled hawkmoth catepillar
"In evolutionary biology, mimicry is a similarity of one organism, usually an animal, to another that has evolved because the resemblance is selectively favoured by the behaviour of a shared signal receiver that can respond to both"...so says Wikipiedia. What this means is that some species evolve to look like others to protect themselves from predators, whether this is emitting similar smells (which is hard for us humans to detect), or here the ability to turn yourself into a snake is a handy one!
I found the caterpillar above in my garden....my family thought it was a snake initially, as it was half covered, swaying about, and quite large, around 6cm long.......so its disguise worked well. Here is another, head on. Certainly looks like a snake with its big eyes to me.