Slime mold

Slime molds are interesting creatures.  They look enough like a fungus that they have typically been studied by mycologists, who study mushrooms.  But, unlike mushrooms, slime molds move.  They're most closely related to amoebas.
     
We came across this one recently at K College's arboretum.  I'm pretty sure it's Fuligo septica (charmingly known as Dog Vomit Slime Mold) which was featured on XKCD.