wrote:
To a naive person, the fungus that grew in my garden that I
couldn't identify might have been taken for a horse or even
field mushroom. It was a suitable shape, with suitable gills,
whitish and the gills went pinkish brown as it matured. But
I think that it was a Hebeloma, all of which are poisonous
(though not lethal). I knew enough to be damn sure that it
wasn't an Agaricus, even if I couldn't tell what it was.

Blimey, they do look similar looking at http://en.wikipedia.org/wiki/Hebeloma
I /have/ grown plain common mushrooms from a kit before (and I have one
still /trying/ to grow in the bathroom, but it's really really not having
it!!), but there isn't much risk going on there. :-}