It's mostly because of choice. [A shrug, but he's saying it more to himself than anything else. Part of him is slowly beginning to understand the Assassins and their choice to assist to allow choice, rather than simply doing his work based on his own agenda.

But he laughs in return when she asks him how he did it.]

He was climbing one of the ledges when I saw him, actually. I say climbing, but it seemed more like he was trying to nearly break his neck by getting up there. So I asked him if he was aiming to do so, and he challenged me to do better.

[Arno looks around him at this point, and sighs.]

I'd show you what exactly I did, unfortunately I don't think trees will be as good a substitute compared to walls and corners.