User blog comment:Xilinoc/Ch. 577 - SWORD/@comment-14244059-20140417182136

Theory: "Drink" isn't actually the release command; it's his Zanpakuto's ability. By telling Nozarashi to drink, it's actually absorbing his reiatsu and grows in size and weight, and therefore in destructive capability.

Personally, I'm still on the band wagon that says "This is makin' me hard" is Nozarashi's true release command...

But in all seriousness, my theory keeps up with the whole "Kenpachi's Zanpakuto is a constant-release" type, doesn't it? It's always been released, he could just never use it's powers because he didn't know how and now he does since he actually sat and had a conversation with Nozarashi.