Homura grimaces, fun? Granted nobody died but... She came entirely too close for comfort. Of Haruko and Kotori had gone without her? Hah, they'd be more victims of that thing for sure. She then turns to Senri in shock, geez has that never come up?
"Not like that, think of them as very nasty shadows that feed on human despair. They live inside of pocket dimensions called barriers, and the one thing all of them have in common is the random murder of humans."
She pauses for a moment, taking a breath and considering exactly how much to explain. Might as well do the whole thing, if only to be safe.
"Beyond that, Witches tend to kill people in two ways, one is by sending their minions out into the world to devour humans, and if those eat enough... They'll become a copy of that Witch. The other is a "Witch's Kiss", those have a wide range of effects at times, but a common one is causing the victim to kill themself..."
Her faces goes a bit dark as the girl holds up her Soul Gem Ring.
"There's another way they're made too, well... If a Magical Girl's gem goes entirely dark, from using too much magic or um emotional problems, then they'd become a witch... Don't tell Sayaka Miki that please, not sure how she'd take it."
She then sighs and looks around, oh no the kid... Well, not like the poor girl has great prospects anyways at this point. Despite that, she'd smile at Kari and wave down at the young girl.
"Um, sorry about all that, I guess you didn't really wanna hear it right? But um, I'm Homura Akemi and it's nice to meet you."