STAR WARS

Wookiee Chow

Far from being a 'psychic' impression, I think Vader is subconciously noting Kenobi's 'style'.
Being attuned to this kind of mental 'indexing' is thought by some to be the source of 'sixth sense' kinds of awareness.
It's easy to believe in Jedi Force training that builds on innate ability in such areas can produce 'masters' with seemingly mystical powers.
Without resorting to mysticism to explain them.

Alternately, it may be Vader himself who has been in direct contact with Kenobi

Kenobi's an old hand at guerrilla techniques and soon they're in the command office off the hanger.

Watch Chewbacca kill a man with one blow like a grizzly bear (death is assumed as the officer never gets back up), making him a murderer as well.

Yet another suspicious line comes out of Kenobi:

So astromech droids are outfitted to hack battle stations?
How does Kenobi know what R2 can do?
And here's something to ponder; Leia's message to Kenobi said that she "placed information vital to the survival of the Rebellion" in R2.
She didn't actually say 'plans for the Death Star'.
Here we see R2 sifting through data while directly interfacing with the Death Star.
Vader has stated openly that the stolen plans were hidden with the droids, but even if R2 is indeed carrying some info, it's very possible that he gets the crucial data about the exhaust port only now.

Case in point, here's a bit of tampering to puzzle over:

In the original movie, the portion highlighted in yellow above is simply NOT there.
In the Special Edition and DVD releases, it is.
In the original, the terminal and machinery in the room can clearly be heard in the background as the readouts are flashed and no one speaks.
In the altered editions, Threepio's voice for this added exposition noticeably does not match his other dialog.
Evidence of tampering is obvious - the reason remains unclear.

It's a stretch to consider that Kenobi has engineered a raid on the Death Star to secure it's blueprints, but he IS a sneaky old bastard.
If he is indeed working with Vader then it becomes more likely that Vader is orchestrating all of this.

Kenobi gives the readouts a cursory once-over, gives a shifty look, and then says that he has to go off alone.
Right, that's far less suspicious than two stormtroopers escorting him around...
Seems to be confident that he can find his way now, eh?
Does he have a Pocket PC with the plans on it, or just the phone number of his contact aboard this battle station?

Before leaving he stops to plant hypnotic suggestions in Luke again.
This is the last time Kenobi speaks to Luke before he 'dies', so he makes it as cryptic and weird as possible:

Always... Remember that, Luke.
There's no escape.