...... "No more studying," Ron sighed happily, stretching out on the grass. "You could look more cheerful, Harry, we've got a week before we find out how badly we've done, there's no need to worry yet."
Harry was rubbing his forehead.
"I wish I knew what this means!" he burst out angrily. "My scar keeps hurting -- it's happened before, but never as often as this."
"Go to Madam Pomfrey," Hermione suggested.
"I'm not ill," said Harry. "I think it's a warning... it means
Ron couldn't get worked up, it was too hot.
"Harry, relax, Hermione's right, the Stone's safe as long as Dumbledore's around. Anyway, we've never had any proof Snape found out how to get past Fluffy. He nearly had his leg ripped off once, he's not going to try it again in a hurry. And Neville will play Quidditch for England before Hagrid lets Dumbledore down."
The phrase "worked up" means agitated or excited. I don't understand why there isn't any conjunction that has been used between the two clauses:"Ron couldn't get worked up", "it was too hot". My best try would be: Ron couldn't get himself excited, because it was too hot there.
What does that sentence truly mean in this context? Why is there no conjunction?
-- Excerpted from Harry Potter.