slime mold.

http://www.colostate.edu/Dept/CoopExt/4DMG/Pests/slime.htm

Thank you Lily, gratefully this is not in my garden but I have sent the link to the neighbor who asked. Hope I don't run into it myself.

Thanks for the informative link.

They are harmless if rather disturbing looking organisms and pop up on any type of dead plant material. They contribute to the
decomposition of dead vegetation and are usually found in soils, lawns and on the woodland floor. In urban areas, they are found on mulch or even in the debris that accumulates in gutters.

I have seen them in fresh delivered bark piles when they are clear, before they are ready to release their spores.
mike