He has astronomical knowledge.

Knock-knock, someone is knocking on the door.

He is interested in ichthyological research.

He cut the apple.

He rejoiced when he heard about the success.

He cautioned not to speak ill of others, saying, 'Illness enters by the mouth, and disaster does not come out of it.'

Moderate exercise is good for health.

The police are investigating the source of the threatening letter.

He headed to the mountain with a rucksack on his back.

Cyclops is a part of Greek mythology.