Dr Karl

Now we're thinking maybe 100 million.

So look up JWST, Just Wonderful Space Telescope, on Wikipedia and it'll give you the latest results.

That's really revolutionising our knowledge of the universe.

In general, what causes you to sneeze is irritation of the cilia in the upper airways.

So let me just talk about that.

So your airways are just a single pipe.

when you get to the back of your throat, and then it goes down into your lungs and it splits into two pipes, one for each lung.

And then it keeps on splitting into four, into eight, and there's 28 generations of splitting before you finally end up with little balls where you have blood running in the wall of the ball.

And there's gas on one side and blood on the other.

And so carbon dioxide leaves your blood and goes into the ball and oxygen goes into your blood.

Now cilia are hairs on your airways that move in an asymmetric motion.

And so they'll move stuff upwards and they're in the first, say, five generations of splitting.

If they pick up dirt, they start pushing it upwards and then they'll set off some irritation that you get rid of it sometimes by swallowing it.

And so during the day you'll sort of go... When you're swallowing something you think...

I know I just swallowed, but why?

And that's stuff that your airways, running by themselves, have shoved up into the back of your throat and you automatically swallowed it and you didn't notice.

Or sometimes it'll make you sneeze.

So sneezing is triggered by the cilia in the top half dozen or so generations of airways to get rid of crud out of your lungs and into the air around you and near all your friends where it belongs.

When you're looking at petrol fumes, normally you've got something in the background such as the sky or a building or a tree.

And the fumes are slightly different from air.