A refresher:

This takes place in the episode where Hakkai's past catches up with him, and Chin Yisou has a puppet that impersonates Goku briefly. Sanzo shoots it, because he can tell the difference between it and Goku.

(The difference is that the puppet never once says the words "I'm hungry.")

When Goku appeared to walk out of the mist, Sanzo's relief was quite possibly one of the strongest emotions he'd ever felt. But then it began to talk.

He had to refrain from flinching when it touched him, or else Gojyo and Hakkai would clue in to something perhaps being wrong, because he wasn't sure. Because it looked so much like Goku, bouncing and bouncing and yet... Something was wrong. Sanzo wasn't sure what.

Damn monkey.

Did he even know something that was impersonating him was running around the forest? If it really wasn't Goku, anyway. But something was wrong, and as soon as Sanzo put his finger on what it was he'd shoot.

Sanzo would be the first to tell anyone that he wasn't much of a friend. That he couldn't be bothered to notice the little things about people. He frankly couldn't care less, and yet.

Well, he knew Goku.

It hadn't taken long, since the stupid kid never shut up. You couldn't not learn everything important about a person like Goku in five minutes. And Sanzo'd had years. Such a long time, especially if you counted all that time with the kid's voice in his head. Calling, calling, calling. Annoying as all hell. Not even in words, just emotions. Sanzo would've ignored it if the pain and loneliness hadn't seeped through to his own mind. (Of course, it wasn't like he'd easily distinguished it from his own. But dammit, he didn't want to feel anyone else's on top of what he already had!)

And then, when he'd actually found Goku, seen him face to face...

It was like finding a part of himself that he'd been missing. Like finding something he hadn't ever known he'd lost. Like meeting up with an old friend. Sanzo had never really called anyplace other than being with his master home, but when he found Goku - well, it was like that.

Maybe, and this was a hell of a stretch, maybe it was something like Nirvana. Except he found it in Goku's gratitude. Goku's... vivacity. Goku's eyes.

So, when something was wrong, Sanzo could tell. But he wanted to be sure. He gave the thing a few more minutes, and thought over what he knew about Goku.

Goku was loud. Goku was exuberant, always talking and talking. Well, so far the thing was doing all right. Goku was cheerful, and warm. Check.

Quickly, quickly, perhaps it will attack.

Goku had a defining character trait! But what? Sanzo could feel the revulsion this thing caused in him, a sort of horror that something could be so like Goku and yet not him. The bile rose in his throat.

Sanzo pushed it away, and thought, and let it tug on his sleeve for a moment longer, finding his gun in his pocket. He was so close to figuring it out, it was practically on the tip of his tongue.

"Let's go," it whined. "I wanna get out of here." Sanzo could mouth the rest of the sentence, if he felt so inclined to waste the effort moving his muscles. I wanna get some food.

Except those words didn't come out of its mouth.

The thing pouted at him, in a way that simultaneously caused a rush of warm familiarity, the feeling of home... and cold, numbing fear for the person whose face that expression actually belonged to. Cold realization.

Goku is not here. This is not Goku. Goku could be... Sanzo didn't finish the thought, instead closed off all attachment he had to this face. Which was, if he was truly honest with himself, a lot. More than perhaps Goku would ever know. More than Sanzo would ever tell him, anyway.

The words came to mind: If you meet a man who claims to be the Buddha, kill him.

He'd just told Hakkai this was his philosophy, hadn't he? Well, if he was to be honest with himself (again) this was the exact opposite. Goku was no Buddha, and it was because of his attachment that Sanzo was shooting this thing.

Well, philosophy and attachments could be damned. He had no particular attachments to philosophy. He did what he did because he wanted to, and that was all.

Sanzo sighed, and drew his gun.