One of the reasons that grass is so unpalatable for humans is its tendency to accrue
silica (the main constituent of glass) as part of its structure. It is particularly
evident at the edges where it can form a formidable array of teeth resembling a saw
blade. Looking closely at the sample of wild grass it is to see how you can get a
nasty cut if you brush against it. The are many different varieties of grass so potentially
a lot of variations to look at, a magnification of around 100x is quite adequate
to see teeth at the edge.