Prospero listened with rapt attention as Sonya described the Tenth and current Vongola Boss. A man like that...could he possibly support Prospero's goal of revenge? It seemed unlikely at the moment, but he wasn't about to be disheartened by that. If anything it meant he would just have to work harder to become the only choice for Naoto's Mist Guardian and ensure that if and when Naoto came to power, Prospero had the means to carry out his own plans.

Things got much more interesting when a man appeared and put a sword to Sonya's throat. The attack certainly came quicker than Prospero could detect, and the fact that this seemed to be a past version of the current head of the Vongola's CEDEF. He tried to seem disinterested as he watched the two of them though. 

"Man.. today keeps getting worse and worse and worse doesn't it? First we have to hang upside down for forever and a half, then some crazy guy from another time shows up and now [I]he's[/I] suggesting our punishment? Next it'll be people from other dimensions popping up." Prospero didn't bother to stop hanging upside down yet, partly because neither Sonya nor Hajime Honda had ordered him to and he didn't want to give anyone an excuse to punish him further. 

For now he simply hung there watching Sonya and the CEDEF head. Getting a glimpse into both his and Sonya's past was invaluable. If he was going to make full use of the Vongola for his plans in the future he would have to know as much as he could about its' members, and insight into Sonya's past might help him survive through training. A slim hope, but still a possibility. In any case, more information was always useful for him. He had no idea if Sonya would oppose his being one of Naoto's Guardians if she figured out his motivations, and trying to figure her out as well as the past-self of this man could be a key to getting what he needed.