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Dueling scars (German: Schmisse) have been seen as a "badge of honour" since as early as 1825. Known variously as "Mensur scars", "the bragging scar", "smite", "Schmitte" or "Renommierschmiss", dueling scars were popular amongst upper-class Austrians and Germans involved in academic fencing at the start of the 20th century. Being a practice amongst university students, it was seen as a mark of their class and honour, due to the status of dueling societies at German and Austrian universities at the time, and is an early example of scarification in European society. The practice of dueling and the associated scars was also present to some extent in the German military.

Foreign tourists visiting Germany in the late 19th century were shocked to see the students, generally with their Studentcorps, at major German universities such as Heidelberg, Bonn, or Jena with facial scars – some older, some more recent, and some still wrapped in bandages.

The sport of academic fencing at the time was very different from modern fencing using specially developed swords. The so-called Mensurschläger (or simply Schläger, "hitter") existed in two versions. The most common weapon is the Korbschläger with a basket-type guard. In some universities in the eastern part of Germany, the so-called Glockenschläger is in use which is equipped with a bell-shaped guard. The individual duels between students, known as Mensuren, were somewhat ritualised. In some cases, protective clothing was worn, including padding on the arm and an eye guard.

The culture of dueling scars was mainly common to Germany and Austria, to a lesser extent some central European countries and briefly at places such as Oxford and some other elite universities. German military laws permitted men to wage duels of honor until World War I. During the Third Reich the Mensur was prohibited at all Universities following the partyline.

Within the duel, it was seen as ideal and a way of showing courage to be able to stand and take the blow, as opposed to inflicting the wound. It was important to show one's dueling prowess, but also that one was capable of taking the wound that was inflicted.

Intonarumori are experimental musical instruments invented and built by the Italian futurist Luigi Russolo between roughly 1910 and 1930. There were 27 varieties of intonarumori in total with different names.

The long and short scales are two of several naming systems for integer powers of ten which use some of the same terms for different magnitudes.

For whole numbers smaller than 1,000,000,000 (10⁹), such as one thousand or one million, the two scales are identical. For larger numbers, starting with 10⁹, the two systems differ. For identical names, the long scale proceeds by powers of one million, whereas the short scale proceeds by powers of one thousand. For example, one billion is one thousand millions in the short scale, while it is one million millions in the long scale. The long scale system introduces new terms for the intervening values, typically replacing the word ending -ion with -iard.

Don't Buy This (also known as Don't Buy This: Five of the Worst Games Ever) is a compilation of video games for the ZX Spectrum released on 1 April 1985. As described on the box, it contains five of the poorest games submitted to publisher Firebird. Instead of rejecting the submissions, they decided to mock the original developers by releasing them together and publicly brand it as "unoriginal" and "awful". Firebird even disowned all their copyright to the game and encouraged buyers to pirate it at will.

Reviews for the game were universally negative, with critics questioning how to critique the game due to its publicity being based on it being a collection of bad games. Despite the negative reception, the game was a commercial success.

The choking game (also known as the fainting game and a wide variety of slang terms) refers to intentionally cutting off oxygen to the brain with the goal of inducing temporary loss of consciousness and euphoria.

Citizenship in a Republic is the title of a speech given by the former President of the United States, Theodore Roosevelt, at the Sorbonne in Paris, France on April 23, 1910.

One notable passage on page seven of the 35-page speech is referred to as "The Man in the Arena":

It is not the critic who counts; not the man who points out how the strong man stumbles, or where the doer of deeds could have done them better. The credit belongs to the man who is actually in the arena, whose face is marred by dust and sweat and blood; who strives valiantly; who errs, who comes short again and again, because there is no effort without error and shortcoming; but who does actually strive to do the deeds; who knows great enthusiasms, the great devotions; who spends himself in a worthy cause; who at the best knows in the end the triumph of high achievement, and who at the worst, if he fails, at least fails while daring greatly, so that his place shall never be with those cold and timid souls who neither know victory nor defeat.

Someone who is heavily involved in a situation that requires courage, skill, or tenacity (as opposed to someone sitting on the sidelines and watching), is sometimes referred to as "the man in the arena".

Pi Day is an annual celebration of the mathematical constant π (pi). Pi Day is observed on March 14 (3/14 in the month/day format) since 3, 1, and 4 are the first three significant digits of π. In 2009, the United States House of Representatives supported the designation of Pi Day. UNESCO's 40th General Conference decided Pi Day as the International Day of Mathematics in November 2019.

Pi Approximation Day is observed on July 22 (22/7 in the day/month format), since the fraction ​²²⁄₇ is a common approximation of π, which is accurate to two decimal places and dates from Archimedes.

Two Pi Day, also known as Tau Day for the mathematical constant Tau, is observed on June 28 (6/28 in the month/day format).

The Karatsuba algorithm is a fast multiplication algorithm. It was discovered by Anatoly Karatsuba in 1960 and published in 1962. It reduces the multiplication of two n-digit numbers to at most ${\displaystyle n^{\log _{2}3}\approx n^{1.58}}$ single-digit multiplications in general (and exactly ${\displaystyle n^{\log _{2}3}}$ when n is a power of 2). It is therefore faster than the classical algorithm, which requires ${\displaystyle n^{2}}$ single-digit products. For example, the Karatsuba algorithm requires 3¹⁰ = 59,049 single-digit multiplications to multiply two 1024-digit numbers (n = 1024 = 2¹⁰), whereas the classical algorithm requires (2¹⁰)² = 1,048,576 (a speedup of 17.75 times).

The Karatsuba algorithm was the first multiplication algorithm asymptotically faster than the quadratic "grade school" algorithm. The Toom–Cook algorithm (1963) is a faster generalization of Karatsuba's method, and the Schönhage–Strassen algorithm (1971) is even faster, for sufficiently large n.

Lignum nephriticum (Latin for "kidney wood") is a traditional diuretic that was derived from the wood of two tree species, the narra (Pterocarpus indicus) and the Mexican kidneywood (Eysenhardtia polystachya). The wood is capable of turning the color of water it comes in contact with into beautiful opalescent hues that change depending on light and angle, the earliest known record of the phenomenon of fluorescence. Due to this strange property, it became well known in Europe from the 16th to the early 18th-century. Cups made from lignum nephriticum were given as gifts to royalty. Water drunk from such cups, as well as imported powders and extracts from lignum nephriticum, were thought to have great medicinal properties.

The lignum nephriticum derived from Mexican kidneywood was known as the coatli, coatl, or cuatl ("snake water") or tlapalezpatli ("blood-tincture medicine") in the Nahuatl language. It was traditionally used by the Aztec people as a diuretic prior to European contact. Similarly, the lignum nephriticum cups made from narra wood were part of the native industry of the Philippines before the arrival of the Spanish. The cups were manufactured in southern Luzon, particularly in the Naga region. The name of which was derived from the abundance of the narra trees, which was known as naga in the Bikol language (literally "serpent" or "dragon").

Headlinese is an abbreviated form of news writing style used in newspaper headlines.