The message
from "JKS" contains these words:

Just googled for slime mould - there was a photo of some at Wimpole a couple
of miles from here. It was similar to what was on my lawn.
How fast does this stuff grow and move? There must have been 5 - 10 ml of
it each time and it appeared in the middle of the lawn overnight.

It will have been there for some time, growing, but it expands with a
heavy dew, wather like snot on your handkie - but in reverse.

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Rusty Hinge
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