It seems a bit wierd, considering the fact that his body is completely mechanical (like a Gen 2 synth, though his mind is more like that of a Gen 3 synth, given his full sentience). So how do stimpaks heal him exactly? You can't regenerate metal.

I normally am pretty good at rationalizing stuff but no idea, really.

Placebo effect?

I got nothing.

And for that matter why does Valentine smoke? Just to look cool I guess.

It's the power of the WAAAAAAGH! at work.

Heh i wud say its probably a bug since they do not work on Codsworth and pre synth body Curie so i wud assume its simply a bug.

He has dialogue for it, so no it is not.

But I'm led to believe Nick is somewhere between a Gen 2 and a Gen 3, maybe he has the proper 'parts,' to be healed with medicine?

Edit: Dude does have skin

Maybe it lubes up his joints and keep him from rusting into place ?

Thats my guess.

I guess for him it acts as a quick fix-it kit to repair whatever damage he sustained.

I know, I'm pulling it out of thin air, but I've got nothing else.