Info about that thing? And oh she knows about Soul Gems, thankfully for Homura, she already knew about that little bit of info.
"Kyubey huh? Well the actual name is Incubator, and I don't really go around screaming from the rooftops about the whole Magical Girl thing but well since it's not a huge secret either..."
She'd then drag the other girl off to the kitchen in fact, speaking lowly at the back of the place and glancing toward the door now and then.
"As for Soul Gems... A lot of us don't even know what those things are lady, I'm one of the ones who knows the details and hasn't gone insane from them, lucky me right?"
She'd sigh and rub at her temple, pulling the glasses off and looking Sakura dead in the eyes.
"You already know enough that I doubt learning more will hurt anyone, so lemme give you a crash course on Incubators I guess. Anything to screw them over honestly. So first up, they don't like explaining anything. Misleading names, not giving full details, whatever they can do to get someone to contract with em. As for their form, they appear as these weird cat/rabbit like things, horribly cute at first glance which is another lure I assume."
Homura then pauses a moment, raising a hand to her chin and thinking on what else this woman might wish to know.
"Oh yeah, the way of signing a contract with them is "fun". See you get to make a wish, a wish that will make everything better really! Except trying to fix your life with magic almost never works, you know right? And finally... See when these cute gems go black, we become what's called a Witch, they're eldritch horrors formed from the grief and despair of magical girls who've lost it entirely. As for a reward... If you happen to see anyone thinking about becoming a magical girl, do me a favor and inform them would ya?"
She begins walking away, stopping for a moment before going back to the main room.
"One last thing, Witches have minions called familiars, those bastards eat enough living humans they become another Witch... Make sure to give out the full story please, if only because I don't want others making half-informed choices like I did."
Finally, she'd walk back out front and put a smile on her face once again as she looks toward Alto, awful quiet all of a sudden.
"Um, is something wrong Alto-kun? If it's about the cake I'm really sorry! And I can always make you something else if you'd like, but beyond that um if you'd like to talk to someone... We don't know each other, but I'm always willing to listen."