Thailog's eyes glow red, when he is in an agitated state, rather than the typical white in male Gargates. This is due to the fact that, prior to this episode Demona was the only female Gargoyle that had been detailed. Since both had been placed in a position as antagonists, Thailog was given red eyes to match Demona's. The full details were not revealed until Angela's introduction, at the beginning of the Avalon World Tour story arc.
Later in The Reckoning, the other clones show the same reversal, revealing it to be a mutation in the cloning process.
"You mean that that creature is still out there? It has the money. It's as powerful as Goliath. And it's SMARTER than you?"
"Owen, I think I created a monster." - Owen and Xanatos