The author says that some grasses contain cyanide, and some don't. He goes on to say it's hard to tell different grass species apart.
And a quote from the article:
While there is no shortage of people on the internet who say grass is edible and nutritious — one Indian claims to only eat grass — the Irish Potato Famine of 1845-49 shows otherwise. Folks were reduced to eating grass yet they died, often with grass stains still on their mouth. Another problem with a grass is that it contains a lot of silica, which wears down teeth. Silica is also not good for our digestive track with a history of causing oesophageal cancer. There is some molecular evidence that our very distant ancestors ate grass, or things that ate grass. It’s a debate but those who study the topic say humans did not begin to advance greatly until they good access to protein, meaning meat. These days grain, the other part of grass, is accused of contributing to bad health and obesity particularly in America. Lastly, in the for-what-it-worth department in Japan men who are not the expected Alpha Male type are called soushoku danshi—literally translated — “grass-eating boys.” If you sprout wheat grass you might want to be careful just who your tell.