In my dream, whenever I even looked at Sans, he looked back at me with that blue and green eyed gaze, and it legitimately started to get kind of creepy to me.
We were in a hotel room together, and Sans hadn't brushed his teeth yet, so his permanent smile looked a little gross. Once his teeth were brushed, it was much better.
Somewhere in the world of my dream lay the Center of Magical Control. Hardly anyone alive even knows about it, let alone gave it a visit. Even most of the Greek and Roman gods are oblivious!
Sans, though, he actually does know about it, and he also knows where it is. He actually makes a visit there once every year. Some people have theorized about what makes Sans so powerful. It's the Center of Magical Control. Going there is what makes him so powerful.
When Percy Jackson found out about that place and went to it, he ran into Sans. When Sans saw him, he dropped his bags out of shock. That's where they were when Sans kept giving Percy the glow eye. Sans was afraid about the secret getting out, and about how much more dangerous Percy's water powers would be.
The demigod was already incredibly powerful, but how much would his powers be enhanced by visiting the Center of Magical Control? Going there just once can boost the power of your magic tremendously. Even when Percy's magic was at its more natural power, he was already a big threat to Sans, who's magic was boosted. With Percy boosted now, too, Sans was at his mercy. Better to keep Percy afraid with the glow eye than to show weakness.