system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do dogs eat grass?
gpt
Your doggie sometimes eats grass to help with tummy aches or if they ate something that didn't agree with them. But dogs and cats also think it tastes yummy, so will occasionally have it as a snack. It doesn't always mean something bad! 

Edit: in your dog's case, he/she may have gotten into the garbage, eaten something bad outside, or may have been fed at a different time than usual. Some dogs just have sensitive stomachs.