I've seen these slimes for a while but never been able to turn on my headlamp camera on in time, I'd assumed that most other ranchers knew about these little buggers, but after talking to a few other ranchers over Starmail, I decided to record them in my own slimepedia entry.
http://imgur.com/a/54TZDAppearance:
A small yellow slime.
Location:
Ranch - Cliffs
Diet:
Fruit
Slimeology:
Watcher Slimes are a very curious species of slime, very few is known about these slimes, as they run away as soon as they are seen. They enjoy watching a rancher's daily life, and are very hard to capture.
Rancher Risks:
The only danger of Watcher Slimes, is trying to find one, most ranchers haven't even seen a Watcher Slime, let alone catch one, so when one is found, most ranchers will behave quite hastily and could hurt themselves in pursuing the slime.
Plortonomics:
Watcher Plorts, once refined, and given an electric current, will make a great motion detector, emitting a very loud noise when anything moves nearby it.
Feel free to PM me with any slime requests, and I'll make you an image of them in the game.