Although humans are the only species that can make fire, communicate through letters and notes, can read a map and can count, our brains do not differ much from those of monkeys and other mammals.
The two biggest differences are that we have more nerve cells in our pleated cerebral cortex than animals, and that our nerve cells are surrounded by a thicker layer of insulation, so that the nerve signals can run faster.
That is why most researchers think that our intelligence is not essentially different from that of animals, but that we have only developed it to a higher level.
Many animals have intelligent traits: they use tools, work together, communicate or take care of peers, but humans do all this to a much higher degree.
However, animal intelligence is difficult to measure because they cannot tell us what they think, so we have to guess what the most intelligent animals are.
Chimpanzees are as intelligent as a child of three, because they can express themselves with sounds, facial expressions and gestures, manipulate and invent snares to benefit from it and understand the order and size of numbers.
Dolphins, such as the bottlenose dolphin, can learn complex tricks, perform them synchronously with other dolphins and pass them on to other species. They can also learn to understand simple artificial languages and express themselves in them.
The Indian elephant can make simple additions: if you have two baskets with 3 and 5 apples respectively (and the elephant can look in the baskets), and then put 2 extra apples in each basket, the elephant will go to the basket with 7 apples walk.
The seesaw crow uses all kinds of tools in the hunt for food. For example, he sometimes throws nuts on a traffic road, so that cars drive over it and the hard caps crack.
The veined octopus or coconut octopus turns two half coconuts into a house, where it hides itself when there is a danger.
The cleaning slip fish does its extra best to rid a fish of parasites if other fish are watching, which may therefore also want to make use of its service.