Original text:

As Wietse moved his face closer to the sphere, instead of seeing his own reflection come closer, all he saw was the reflection of gis desk and the door behind him, but not of himself.

Wietse moved away from the sphere in confusion, accidentally knocking over his plastic cup of warm cocoa. Ah, damn! Ah, never mind.

Wietse moved closer to the sphere again. Where was his reflection? It was almost as if Wietse had been a vampire from one of those old vampire movies. Wietse took a large magnifying glass out of his desk's drawer and started to look closer at the sphere.

Then the sound of the doorknob turning. Wietse quickly placed an upside down cardboard box over the hovering sphere in order to obscure it from sight, just in time before his guard entered the room.

I think this section would flow more smoothly if the first 2 paragraphs were merged into one, and last 2 paragraphs were also merged into one. After merging and correcting for typos and grammar errors (noted in bold), the text should read:

As Wietse moved his face closer to the sphere, instead of seeing his own reflection come closer, all he saw was the reflection of his desk and the door behind him, but not of himself. Wietse moved away from the sphere in confusion, accidentally knocking over his plastic cup of warm cocoa. Ah, damn! Ah, never mind.

Wietse moved closer to the sphere again. Where was his reflection? It was almost as if Wietse had been a vampire from one of those old vampire movies. Wietse took a large magnifying glass out of his desk's drawer and started to look more closely at the sphere. Then, he heard the sound of the doorknob turning. Wietse quickly placed an upside down cardboard box over the hovering sphere in order to obscure it from sight, just in time before his guard entered the room.