Here are the corrected sentences and a simple explanation:
Original: Hyenas look like dogs but they are in fact distant cousins of cats. When they laugh, they sound like us.
Corrected (simple): Hyenas look like dogs, but they are actually distant cousins of cats. When they laugh, they sound like us.
Why?
- The first sentence has two complete ideas, so we put a comma before "but" to join them: "Hyenas look like dogs, but..."
- "Actually" is an easy word to use instead of "in fact." If you keep "in fact," put commas around it: "...but they are, in fact, distant cousins of cats."
- The second sentence is already correct. When a sentence starts with "When they laugh," we put a comma after that beginning part.
Final version to read aloud: Hyenas look like dogs, but they are actually distant cousins of cats. When they laugh, they sound like us.