Foxtail alert! They are dangerous to dogs.

[Catherine]

Foxtails are a grassy weed whose seeds are very dangerous to dogs. If they try to eat them,  they end up stuck in the mouth or throat. In some cases they can migrate deeper into the body and do serious damage. 

https://www.cbc.ca/news/canada/saskatche...-1.5693589

Once you suspect foxtails a visit to the vet is necessary. I guess I grew up knowing foxtails are dangerous, They are spikey and barbed.
I think with plants, if you are not sure, it is best to keep your dogs away from them. There are other plants out there that can cause trouble.
Let dogs stick to nibbling grass and leave the bigger weeds alone.