Arcane Bond Great concept ... in need of clarifications

[The Wraith]

Regarding the sentence:
"A bonded object can be used once per day to cast any one spell that the wizard knows and can cast, just as if the wizard had cast it. This spell cannot be modified by metamagic feats or other abilities. The bonded object cannot be used to cast spells from the wizard’s prohibited schools."

I think that the Arcane Bond 'casts by itself' a spell (much like an Imbued Familiar, or a Familiar with a Spell-like ability), but at the cost of a swift action of the Wizard - obviously, if I'm wrong, I would be happier (this smells like cheese...) and correct this in the future.

So, is there any clarification on this? The high-level Wizard my group and I playtested made clever use of this 'swift' spell cast from the Arcane Bond, but I'm not completely sure this was the intended idea...

[DougyP]

My confusion is on the wording "capable of casting" Does this mean that I can cast anything in my spell book? I am certainly capable of casting anything in my spellbook. Or does it mean anything I am capable of casting AT THE MOMENT, which would mean that only spells that I have prepared and HAVE LEFT for the day.

I was assuming the later, or is it something else entirely?