# Some questions about simulator in UC proof

Let's focus on the UC proof in the existence of the dummy adversary $$\mathcal{D}$$ and the simulator $$\mathcal{S}$$ that internally runs $$\mathcal{D}$$. My questions are:

1. Is it true that $$\mathcal{S}$$ can only see that the environment sends input to some real world corrupted party via $$\mathcal{D}$$ while $$\mathcal{S}$$ has no idea about the content of the input? Otherwise there is no need for $$\mathcal{S}$$ to extract the input of corrupted parties.
2. Assume that there are two corrupted parties communicating with each other via authenticated channel in real world protocol. Is it true that $$\mathcal{S}$$ can obtain their messages from the authenticated channel (or, from $$\mathcal{D}$$)? Does $$\mathcal{D}$$ relay messages between these two corrupted parties as the real adversary in protocol execution?
3. Can $$\mathcal{S}$$ see the message (including its header and content) sent from some corrupted main party to the environment in real protocol execution?

Many thanks.