As can be seen in the first photograph, there's a S-shaped chain of "chippings", which might resemble a tail, a long neck or... I don't know what. Maybe someone sometime was bored and practiced stone hewing.

The "chippings" are about 3 to 6 mm deep and while not identical, quite similar in shape and size. Their arrangement looks to me rather organic, but I am no expert.

For completeness, this is the back side of the piece of slate.

I know that slate deposits tend to contain fossils and wonder if I got lucky, or if I am seeing something that isn't there.