"It's my Patronus," William said absently, because he knew the significance of a mongoose of all animals when it came to him personally, and oh, oh. If he wasn't having a drug flashback after all, then the memory and then pull of magic suddenly made a lot more sense. Particularly in a larger context, because everyone at school had known what Pete Wentz's Patronus was. The older Ravenclaws had disdainfully sniffed about it in the common room whenever Pete had been prone to bouts of teenage strutting. He'd even had a nickname up in their tower, seventh-year. Rex Leo. King Lion.
He walked in so that Pete could close the door, and the mongoose darted forward to investigate Pete's lion, raising its pointed nose into the air very close to the lion's rather large and carnivorous mouth. William was slightly wary on that account, but his brain was busily occupied with this newly-presented puzzle. He didn't think you could involuntarily conjure a Patronus, but it appeared that they had. And yet...
He pointed at the startlingly corporeal creatures taking up space on Pete's carpet and refusing to be wispy silvery shapes of mist by any stretch of the imagination. "Those aren't Patroni."