When Miel tossed the rat into the bushes, he had decided to come clean after a while. However, he didn't know that Larkin would catch him red-handed. Moreover, the rat might still be around. Even if he could choose to lie to Larkin, he knew it very well that Larkin could detect lies. If he dared to lie, he would be in more trouble.
That was why he geared up his courage in his heart. It was better to just tell the archduke his real thoughts about having the rat around and how dangerous it was for the archduke to begin with. As long as he didn't lie or twist his words, he was already taking half the punishment.
"Your Grace, I…" Miel opened his mouth, but he forgot to rehearse what to say first. Should he greet the archduke, or should he jump into the question already? Regardless of his choice, how should he put his actions? Should he sound defensive or matter-of-factly?