Further to Peter's mention of the spikey things here in Oz, they would be the Cat Head Burr or Three Cornered Jack, which is a seed of an evil creeping weed. Very common where I live, unfortunately!
Whichever way these fall or lie, there is always one spike vertical and ready to get you!
These are capable of puncturing motor bike tyres and especially those on the Postie's bikes, and these tyres run "green slime" constantly as a puncture preventative.
They do terrible things to pushbike tyres and go right through rubber thongs ( Flip Flops ).
Ian.