As a southerner I've been barefoot a lot over the years and it's no fun to step on those things ... one time our dog stepped in a patch and really yelped ... they really do hurt! It also is no fun trying to get the barbs out because that's painful too. I see we have a few Cenchrus listed in the ATP database: http://garden.org/plants/searc...
~ I'm an old gal who still loves playing in the dirt!
~ Playing in the dirt is my therapy ... and I'm in therapy a lot!