Reagan didn't notice it at first. They were at the park, their sketchbook on their knees, drawing the pigeons and the people walking by. Since they weren't listening to the people around them, there wasn't a chance for them to realise that their words were becoming gibberish to them. Instead they first noticed that something was wrong when their phone buzzed with a message.

They grab it from their pocket and turn the screen on. And then they stare at the message. Reagab rubs their eyes and looks at it again. It is still incomprehensible. They pause.

They slept well the previous night, they're quite sure of that. Which means that the letters aren't failing to have meaning due to sleep deprivation. That would be a nice and simple explanation with an easy solution, and therefore much better than whatever is happening!

Maybe it's a prank? Some sort of nonsense made-up alphabet that a friend is sending joke messages in. Unfortunately, opening the chat makes it clear that that isn't the case. Every previously sent message is just as non-sensical looking as the last one. (And not just the messages, anything written, including the time is indecipherable. Symbols that feel like they should have meaning but which Reagan can't understand).