Funny, but this...
http://www.punchcartoons.com/p782/Cartoon:-I-keep-thinking-it's-Tuesday'-Hippo-Sketch./product_info.html
while utterly irrelevant is the funniest cartoon in the world, though you may disagree.

Can't see why it isn't fear of ducks in general.

Anatidospectophobia would be nearer the mark, though that might mean fear of watching ducks rather than of ducks watching.

One of the physicists at the Manhattan Project built one of these - for the life of me I can't remember which one, though. Could have been Feynman - I'll have to dig out my Project Orion book where I read it.

Nuking it might be a really risky option. For a start, there's nothing to push against, so it's hard to change its course. If you succeed in smashing it, we just get hit with several deadly meteorites instead of one - breaking it won't change the trajectory of the fragments by much.

A better option might be for long slow thrust starting as soon as possible. Keep it in one bit and steer it into a near miss. If it already looks like it's going to miss, steer it a bit further just in case.

That's a a walking aid, for non-British readers.

A really impressive build, with some splendid skills well demonstrated. Found the video at the end rather disappointing - I know it ain't going to move like a young agile tantaun, but it looked more like it needed a zimmer frame.

Spats - so, they're not all that much better than a car, in terms of fuel consumption. For their weight and size you'd expect them to use a quarter of the fuel, not half.

"The aim was to explore nuclear bombs for non-military uses, " - that sounds rather specious. More likely it was a rather lame excuse for continuing to test munitions in an irresponsible way.

Few bikes manage more than 70mpg - the tiniest scooter can barely manage a reliable 100mpg - when you consider how much heavier a car is, that ain't great.

How splendid!

Some are more effective than others, of course, but they're wonderful.

Larfin - oh, it's nothing particularly clever, particularly when you know how to do it.

Early arches were semicircular. Later arches introduced pointed arches made from two circle segments leant against each other to give long tall windows. Finally, for bridges, someone realised that you don't have to have a semicircular arch - which makes the bridge too high for people to easily cross without expensive ramps leading up to it, but that you can flatten the arch to leap a far wider span without the height penalty.
Most stonework river bridges are elliptical arches.

Motorbikes often have appalling fuel consumption. On a long gentle run I can get 50mpg (that's British gallons, of course) from my car - considering how limited they are few bikes can get twice that - you'd expect them to get way way more -but they don't.

Malachite was one of the three I would have got right just from the name. I'd heard of gamboge but wouldn't have had a clue what it looked like.

I love it - like many good designs it's an elegant solution to a problem. More, it's the sort of solution that's only obvious once you've seen it done.

Like the elliptical arch. For centuries no one thought of it - but once someone did it was obvious. If you could just say to an early medieval builder "elliptical arch" he'd like as not immediately grasp what you meant - all the pieces were there but no one made the leap.

I'm surprised that an off-the-shelf plane like that can cope with the extra weight and drag - they're not usually overpowered. Then again it's fairly easy to fit a more powerful motor...