A Quote from Portal 1
GLaDOS
While it has been a faithful companion, your Companion Cube cannot accompany you through the rest of the test. If it could talk - and the Enrichment Center takes this opportunity to remind you that it cannot - it would tell you to go on without it, because it would rather die in a fire than become a burden to you.
More quotes from Portal 1
The Enrichment Center is required to remind you that the Weighted Companion Cube cannot talk. In the event that it does talk The Enrichment Centre asks you to ignore its advice.
Area and state regulations do not allow the Companion Cube to remain here, alone and companionless.
Time out for a second. That wasn't supposed to happen. Do you see that thing that fell out of me? What is that? It's not the surprise. I've never seen it before! Never mind, it's a mystery I'll solve later... by myself, because you'll be dead.
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!
Please note that we have added a consequence for failure. Any contact with the chamber floor will result in an unsatisfactory mark on your official testing record, followed by death.