The ninja stopped behind Usopp, turning his attention to the man at the door as well and narrowing his eyes. If he'd had better control of chakra here, he would have been able to tell this much easier. As it was, it still seemed more like the source of the heavy aura was beyond the door, not standing in front of it. He was pretty certain of it.

"No," he replied, still staring at Clark. "I don't think it's him." Sai didn't have much ability where it came to sensing threats just by appearance, but even so - this man didn't look particularly threatening. He seemed about as confused as his pirate companions.

Feeling confident enough of this now, the ninja smiled at him. "Hello."