Angel had felt bad about Oz being locked down there all by his lonesome, and being that Zuko was showing a surprising amount of contribution to the team by seeing to the needs of their current customer, the vampire wandered down the the caged area of the basement to give the werewolf some company.
He hadn't been down there since his last stint as Angelus, when the being that had possessed Cordelia convinced the former members of his team to get a shaman to pull his soul from his body. It had taken a lot of effort of the team's part to get him back in this cage, a visit from Willow curtesy of Fred to restore his soul, and nearly cost Faith her life. He was not ready to relive anything like that again, not ready to be the reason people's lives were tormented, but venturing back down into that part of the basement wouldn't hurt anything.
Unfortunately for Angel, he was wrong and he was about to be hurt.
"Oh boy," escaped Angel's mouth as he found himself face-to-face with the snarling werewolf that was once Oz.