Being called “mule-headed” might not be such a bad thing.

An English biologist tested the cognitive skills of horses, donkeys and mules (bred from a male donkey and a female horse) and reported that mules are smarter than their parents.

Six of each animal were shown sets of two food buckets, each bucket marked with a different symbol. To obtain the food, the animals had to pick the bucket with the correct symbol. The mules, reports Leanne Proops of the University of Sussex, learned to differentiate between more sets of symbols and do it more consistently than either donkeys or horses.

Proops attributes mule smarts to “hybrid vigor,” in which the best genes of each parent mix and match to produce young with superior traits. The physical benefits of hybrid vigor in mules are well-known: They tend to be bigger and stronger than either parent. But this is the first time research has suggested an intellectual benefit.

Alas, there's a downside. Mules are sterile, so any improved hybrid smarts can't be passed along to their young.

VERBATIM

You can't fake urine.

– John Lewis, head of life-support systems for the proposed Orion space capsule program, on NASA's request for employees' urine. Capsule designers say they need the real stuff to figure out how to store and dispose of it on future space missions

BRAIN SWEAT

Unscramble this word: GORNSIMMAROCI

PRIME NUMBERS

31 – Percentage of endangered birds in the United States that are indigenous to Hawaii

4 – Percentage of money spent on saving U.S. endangered birds that is spent on species in Hawaii

23 – Number of Hawaiian bird species that have gone extinct since arrival of Europeans in 1778

17 – Number of remaining bird species with populations fewer than 1,000 individuals

Sources: New Scientist; David Leonard, Hawaii Division of Forestry and Wildlife

'TRUE FACTS'

The world's first official bumblebee sanctuary has opened near Loch Leven in Scotland. Supporters hope the protected, flower-rich meadow will counteract extensive habitat loss elsewhere. In recent years, three European bee species have gone extinct.

ANECDOTAL EVIDENCE

In 1921, on a visit to Boston, Albert Einstein was dining with city leaders as newspaper reporters watched. Occasionally, one of the reporters would yell out a question. One of those questions was, “What is the speed of sound?”

Einstein professed he didn't know, a knowledge gap that the local papers prominently noted the next day. Einstein himself didn't seem embarrassed.

For the record, the speed of sound is variable, depending upon the medium the sound waves are passing through. In dry air at sea level, the speed of sound is roughly 761 miles per hour. Given his famous equation E=MC² (energy equals mass times the speed of light squared), Einstein would presumably have fared better if someone had asked him the speed of light. It's 186,282 miles per second in a vacuum.

JUST ASKING

Would you still be hungry if you ate pasta and antipasta?

BRAIN SWEAT ANSWER

MICROORGANISM

SURELY YOU'RE JOKING

A biologist was doing some field work when a frog called out to him and said: “If you kiss me, I'll turn into a beautiful princess.”

The biologist picked up the frog and put it into his pocket. The frog spoke up again: “If you kiss me and turn me back into a beautiful princess, I will be your loving companion for an entire week.”

The biologist took the frog out of his pocket, smiled at it and returned it to his pocket. The frog cried out: “If you kiss me and turn me back into a beautiful princess, I'll stay with you for a year and do anything you want!”

Again the biologist took the frog out, grinned, then moved to return the frog to his pocket. The frog balked, yelling: “What's the matter? I've told you I'm a beautiful princess, that I'll stay with you for a year and do anything that you want. Why won't you kiss me?”

The biologist replied: “Look, I'm a scientist. I don't have time for a girlfriend. But a talking frog – now that's cool.”

ANTHROPOLOGY 101

Among the Marvas of India, an arranged wedding could not be stopped. If the bride or groom died before the ceremony, the other person would be married to the corpse, but was free to find a living partner afterward.

THIS WEEK IN SCIENCE

This week in 1883, Mount Krakatoa, an island volcano in the Dutch Indies (now Indonesia) erupted, destroying two-thirds of the island and producing huge tsunami waves that swept across the immediate region. An estimated 36,000 people were killed.

Krakatoa's blast is considered the most violent known blast in human history. It was loud enough to be heard in Australia; the shock wave registered on English barometers. The massive amount of volcanic dust spewed into the atmosphere by Krakatoa eventually circled the world, blocking sunlight and altering weather patterns for several years.