"One Eye Open" effect?

[Opuk0]

One Eye Open reads as follows:

Spoiler:

The DCs of your Perception checks don’t change when you are asleep. If you succeed at a Perception check to notice something dangerous while asleep, you can wake up to confront the danger.

The first part is obvious enough in intent, it's the second part that caught me off-guard.

Is the implication that if you don't have this feat and still manage to beat the perception DC you aren't physically capable of waking up? Or is it just that you wake up on the same turn as the stimulus that triggered the perception check?

[Jeff Merola]

I think the intent is that it lets you, well, recognize the intent. Without the feat you'd still wake up, but you might not immediately recognize the situation as dangerous. With the feat you'd wake up and immediately know that you're in danger, and thus be able to react immediately.

[Diego Rossi]

PRD wrote:

One Eye Open

Prerequisite(s): Wis 13, Alertness.

Benefit: The DCs of your Perception checks don't change when you are asleep. If you succeed at a Perception check to notice something dangerous while asleep, you can wake up to confront the danger.

Normal: The DC for any Perception check attempted by a sleeping creature is increased by 10.

Linking or citing the whole text help. What say "Normal"?

"Normal: The DC for any Perception check attempted by a sleeping creature is increased by 10."
Nothing about not be able to react when you wake up.
So the second part is there to reiterate what already happen when you perceive something while asleep: you wake up.