Spacetime engines always work in pairs.

Engine number one and engine number two. The child is the product of their union. And three and four mark the door. It must be so.

The engines grow accustomed to one another. Should one of the pair require replacement, the widowed unit must be spun down and reset. It will not cleave to any other engine, otherwise.

In order that they may work together, the engines must remain in synchrony. They communicate with one another by way of the cables.

In idle moments they will play together. Strategy games, sometimes. They will choose a nonstruct region and fill it with an entire universe. There, entire civilizations will be born, live, and die.

I eavesdrop on them to see what they're up to. If you turn inspect mode on and run the data through an interpreter, you can hear them sing sometimes.

They actually sing!...