Corrected sentence: When it hides, a baby rock partridge stays very still and looks like a small striped stone.
Why this is better (easy steps):
- Start with When it hides — this makes the sentence sound clearer than To hide.
- Stays very still tells us how it hides (it doesn’t move).
- Use and to join the two ideas: it stays still and it looks like a small striped stone.
- No comma is needed between small and striped.
Another simple version: A baby rock partridge hides by staying very still. It looks like a small striped stone.