Earth: mostly harmless

You just come along with me and have a good time. The Galaxy's a fun place. You'll need to have this fish in your ear.

The available worlds looked pretty grim. They had little to offer him because he had little to offer them. He had been extremely chastened to realize that although he originally came from a world which had cars and computers and ballet and Armagnac, he didn't, by himself, know how any of it worked. He couldn't do it. Left to his own devices he couldn't build a toaster. He could just about make a sandwich and that was it.

The teacher usually learns more than the pupils. Isn't that true? "It would be hard to learn much less than my pupils," came a low growl from somewhere on the table, "without undergoing a pre-frontal lobotomy."

...they discovered only a small asteroid inhabited by a solitary old man who claimed repeatedly that nothing was true, though he was later discovered to be lying.

A computer chatted to itself in alarm as it noticed an airlock open and close itself for no apparent reason. This was because Reason was in fact out to lunch.

It is difficult to be sat on all day, every day, by some other creature, without forming an opinion on them. On the other hand, it is perfectly possible to sit all day, every day, on top of another creature and not have the slightest thought about them whatsoever.