In a series of experiments, the elephants first explored the mirror -- reaching behind it with their trunks, kneeling before it and even trying to climb it -- gathering clues that the mirror image was just that, an image.

That was followed by an eerie sequence in which the animals made slow, rhythmic movements while tracking their reflections. Then, like teenagers, they got hooked.

All three conducted oral self-exams. Maxine, a 35-year-old female, even used the tip of her trunk to get a better look inside her mouth. She also used her trunk to slowly pull her ear in front of the mirror so she could examine it -- "self-directed" behaviors the zookeepers had never seen before.

Moreover, one elephant, Happy, 34, passed the most difficult measure of self-recognition: the mark test. The researchers painted a white X on her left cheek, visible only in the mirror. Later, after moving in and out of view of the mirror, Happy stood directly before the reflective surface and touched the tip of her trunk to the mark repeatedly -- an act that, among other insights, requires an understanding that the mark is not on the mirror but on her body.

Kate Arnold and Klaus Zuberbühler, of the University of St Andrews, have now observed the monkeys using these sounds in a new way. A particular sequence of pyows and hacks appears to mean something entirely different.

The monkeys live in groups consisting of a single adult male accompanied by several adult females and their young. When the male utters this “sentence”, consisting of up to three pyows followed by up to four hacks, it seems to be a command telling others to move,generally to find safer, less exposed terrain.

They use the signal not only when predators are around, but also during ordinary activities such as foraging. It seems to mean "let's get out of here".

The research is published today in the journal Nature. Dr Arnold said: "These calls were not produced randomly and a number of distinct patterns emerged. One of these patterns was what we have termed a pyow-hack sequence. This was either produced alone or inserted at certain positions in the call series."

Luke burst onto the science scene aged 8 and his CV is now two-pages long. For his latest experiment, he used goniometry (the science of measuring joints) to investigate how rock climbers can avoid muscle strains.

"I was rock climbing and my arms started to hurt," he said. "I was only climbing for three minutes. So I was like, 'How can you fix this?' Then we walked through St Vincent de Paul and I saw a book on goniometry." Luke studied rock climbers' positions, found correlations between repetitive movements, then designed a measuring device to work out how to reduce repetitive strains. If climbers were then educated about these strains and could use different movements, he concluded, they should be able to reduce tendon, ligament and muscle problems. The project won a national Australian Association of Mathematics Teachers' award.

The scientists said they had seen gorillas use tools to navigate swampy ground.

One gorilla reportedly used a stick to test the depth of a puddle in her path.

Another is said to have been seen using a tree trunk as a support while digging for herbs, and as a bridge to cross swampy ground.

"This is a truly astounding discovery," team leader Thomas Breuer said in a statement quoted by the Associated Press news agency.

A biologist that works with the animal said it has been curious since birth.

He said the lid-removing octopus is probably the most intelligent animal at the aquarium.