Mysterious caterpillar (?) spotted this afternoon

All My Friends Are Insects The Diary of Lupin Pooter

S. and I were on our way somewhere when the slow and gentle undulatory motion of a caterpillar caught my eye.

We paused for a moment, I took a short bit of video of the thing zoomed-in as much as possible without reducing the bug to a blur, and then we continued on our way. Perusing the video later, the wee beastie looks even stranger than it appeared at the time.

A few seconds’ worth of shakycam video of a very odd-looking caterpillar (or perhaps not a caterpillar at all) traversing a ceramic tile outdoors.

Its dorsal surface was studded with what look like a series of dark green or brown lumps, including one large circular knob with smaller hemispherical bumps located about half the way down its back that seems to project upwards on a stalk.

None of the caterpillars featured on iNaturalist’s Common Caterpillars of Hong Kong list bear much resemblance to this critter and I struck out after plugging terms and phrases that seemed applicable into Google Image Search. It’s not a head-stacking caterpillar because the lumps aren’t all on top of its head and aren’t a series of progressively smaller head-shaped things. Neither do the bumps appear to be tussocks (closely-packed patches of upright hairs) or spines. The creature seemed vigorous and healthy, so I’m disinclined to interpret the shapes as parasites or freeloaders.

Maybe somebody on the Reddit, What’s This Bug? subreddit can solve this mystery. Here’s my ident-request post: Knobbly-backed caterpillar(?), 2-3cm long, spotted traversing a pavement in Hong Kong..

Next-day update: Trying a different subreddit.

My first Reddit post didn’t elicit any responses, so I gave it another shot, this time at the bugidentification subreddit: What is this? It appears to be a caterpillar (?) with dorsal knobs (overall length 2-3 cm). Spotted in Hong Kong.

Six days later…

My 2nd Reddit post garnered a few upvotes, but no replies. These screenshots are from a couple of days ago, but I checked both threads again just now and nothing has changed.

Screen captures of my two unsuccessful bug-id subreddit Reddit threads (click for a larger version).
Screen captures of my two unsuccessful bug-id subreddit Reddit threads (click for a larger version).