Momentum, a function of mass and velocity, is conserved between portals. In layman's terms, speedy thing goes in, speedy thing comes out.

This is your fault. It didn't have to be like this. I'm not kidding, now! Turn back, or I will kill you! I'm going to kill you, and all the cake is gone! You don't even care, do you? This is your last chance!

As part of a required Enrichment Center protocol, the previous statement that we would not monitor the test area was a complete fabrication. We will stop enhancing the truth in three... two... zzzt

Did you know you can donate one or all of your vital organs to the Aperture Science Self Esteem Fund for Girls? It's true!

There was even going to be a party for you. A big party that all your friends were invited to. I invited your best friend, the Companion Cube. Of course, he couldn't come because you murdered him. All your other friends couldn't come, either, because you don't have any other friends because of how unlikable you are. It says so right here in your personnel file: "Unlikable. Liked by no one. A bitter, unlikable loner, whose passing shall not be mourned. Shall NOT be mourned." That's exactly what it says. Very formal. Very official. It also says you were adopted, so that's funny, too.