Where is a sound? If I play a note at the piano, you and I both seem to locate it at the instrument. But we both also know that we perceive the note because the piano sends waves through the air that strike our ears. That would mean that most of our auditory perception is illusion. Is that what we want to say?

Philosopher George Berkeley wrote, “When I hear a coach drive along the streets, immediately I perceive only the sound, but from experience I have had that such a sound is connected with a coach, I am said to hear the coach.” Perhaps the sound lies at our ears, or at our sensation of it, and it’s only our experience of the world that leads us to attribute it to some remote source. But that raises problems of its own. If sound is sensation, then can a sound occur if no one is present to hear it?

Perhaps the answer lies in between: Acoustics tells us that sounds are vibrations transmitted by the air. But vibrations of very high or low pitch aren’t perceptible to human ears. Are these still sounds?

A similar puzzle concerns smells.

Just an oddity — in Nature, June 5, 1919, Cambridge zoologist John Stanley Gardiner notes that a Fiji harbormaster had informed him of a saltwater crocodile that had landed alive on Rotuma, 260 miles to the north and 600 miles east of the New Hebrides.

“It certainly did not come from Fiji or any lands to the east, as crocodiles do not now exist on them,” Gardiner wrote. “It must indeed have crossed from the west, and covered at least 600 miles of open, landless sea.

“This occurrence is sufficiently remarkable to be placed on permanent record.”

Something significant happened in Tandil, Argentina, on Feb. 29, 1912 — a 300-ton stone that had perched impossibly on the edge of a local hill suddenly tumbled to the bottom and broke into pieces.

Whether this happened due to vandalism or to blasting at a local quarry is unknown — there were no witnesses.

In 2007 the town replaced it with an exact replica. To date, it’s still there.

Stranded in Java after the Japanese invasion of 1941, the Dutch minesweeper Abraham Crijnssen found a unique way to sneak out: The crew covered the decks with jungle foliage and painted the hull to resemble cliffs, giving the ship the appearance of a small island.

Traveling only at night and anchoring near shore, the minesweeper gradually made her way to West Australia, becoming the last Allied vessel to escape Java and the only one of her class in the region to survive.

(Thanks, Paul.)

Germany’s Heidelberg Castle is home to a famously enormous wine barrel, capable of holding 57,853 U.S. gallons. This is actually the most recent of four enormous wine barrels that the castle has housed, the first built in 1591. Unfortunately it’s empty — today it serves mostly as a tourist attraction and a foundation for the fanciful dance floor above it.

“Everybody has heard of the great Heidelberg Tun,” wrote Mark Twain in A Tramp Abroad, “and most people have seen it, no doubt. It is a wine-cask as big as a cottage, and some traditions say it holds eighteen thousand bottles, and other traditions say it holds eighteen hundred million barrels. I think it likely that one of these statements is a mistake, and the other is a lie. However, the mere matter of capacity is a thing of no sort of consequence, since the cask is empty, and indeed has always been empty, history says. An empty cask the size of a cathedral could excite but little emotion in me.”