Corrected sentence (easy to read):
Hippos are herbivores. That means they eat plants, mostly grass.
Why this is better (simple steps):
- We split the idea into two short sentences so it is easier to understand.
- "That means" explains the word "herbivores."
- "Plants, mostly grass" tells what they eat and gives grass as an example.
Quick tip: You can also say it all in one sentence and it is still correct: "Hippos are herbivores, which means they eat mostly plants like grass."