Tristram Goodman studied common sense with a man he met in a cave when out fellwalking. The cave was in a disused quarry. It was cold inside but was beautifully lit with a green glow from the radioactive Radon rock.
It was a very beautiful cave as you may imagine.
Two hundred metres in was a hole in the floor, about the size of a standard toilet. Here, walkers who dared to come this far into the glowing cave, could crouch in the French way and have a crap.
The hole was said to be bottomless, so no one knew what happened to the turds once gravity got hold of them; actually, no one really gave a shit.

Tristram crouched and did his business. His business, a healthy eight incher (not his commercial business) then fell into the darkness. It fell, and fell, and fell … and fell, and fell and fell.

But, there was something very strange about this hole.
The hole went right through the earth and ended up in the centre, proving the centre wasn’t molten, which had dire consequences for science who had bullshitted about it for yonks. When it got to the centre, the business had to think quickly, because now the only way was up; in fact, down was up i.e. common sense.
It just followed the hole as it had to and kept falling down to Australia; which was actually up, as the business, when it popped out couldn’t shoot down, hundreds of metres up into the sky (could it? Common sense?).

The business (an eight inch turd remember), using the speed of its decent descent to the centre of the earth eventually shot thousands of metres into the outback sky. It reached its zenith and paused for a few seconds. It wished it had eyes because it could then have taken in the view. And then it began its second decent descent. It thought ‘two decent descents and a butt-clenching ascent in one day!’ … it also thought ‘beats Tristram Goodman’s dark, damp innards’.

It is quite boring being an alien as there is no real entertainment on mother ships; abduction crews and UFO sighting ships have all the fun. That’s why they had drilled the hole with a special, gravity altering drill. The aliens loved to gather around the big screen and watch the stool’s descent from the sky. They would take bets whether the stool would land on an old Aussie woman’s head, an old man’s head, a cat, dog, kangaroo, wallaby, Aborigine etc.
In this case it was an old woman, their favourite target, which caused a huge cheer on the bridge.

Tristram finished and wiped his butt with a tissue, which he dropped into the loo-hole. The tissue, being very light would take ages to fall and would probably never rise to Australian soil.

Where have all the tissues gone
Long time passing
Where have all the tissues gone
Not so long ago
Where have all the tissues gone
The centre of the earth, every one.

“Very good, you hit an old woman on the head” said the voice. Tristram turned around and there, in the green glow of the cave walls stood a man, maybe in his thirties.
“Who are you?” asked Tristram.
“I’m the leader of the aliens, I have a plush room behind the cave wall. As you’re human, obviously; I wondered if you would like to learn common sense and go teach it to your people. I think they would benefit from it. How about it? We need a laugh.”
“How would I get here for lessons? I live miles away.”
The alien leader handed Tristram a special phone, “use this, you call me and I’ll send a ship out to pick you up; and drop you off afterwards of course.”

And Tristram Goodman slowly became a human common-sense guru; the only one in the world (obviously then, the best).