The "Clever Hans Phenomenon" revisited.

In the first decade of the 20th century, a horse named Hans drew worldwide attention in Berlin as the first and most famous "speaking" and thinking animal. Hans solved calculations by tapping numbers or letters with his hoof in order to answer questions. Later on, it turned out that the horse was able to give the correct answer by reading the microscopic signals in the face of the questioning person.

The magical number four: A biological, historical and mythological enigma.

Precise recognition of small object numbers without counting is a widespread phenomenon. It is well documented for humans and for a series of non-human vertebrates. Recently this has been confirmed for an invertebrate, the honeybee.

To bee or not to bee, this is the question…: The inborn numerical competence of humans and honeybees.

Human inborn numerical competence means our ability to recognize object numbers precisely under circumstances which do not allow sequential counting. This archaic process has been called "subitizing," from the Latin "subito" = suddenly, immediately, indicating that the objects in question are presented to test persons only for a fraction of a second in order to prevent counting. In contrast, however, sequential counting, an outstanding cultural achievement of mankind, means to count "1, 2, 3, 4, 5, 6, 7, 8…" without a limit.

Give me 5…The invention of number five in ancient civilizations: A consequence of our limited inborn numerical competence.

Precise recognition of small numbers of objects without counting is an archaic, inborn ability of humans. Since almost 140 years it is known that we can recognize precisely only up to four objects if sequential counting is prevented. Vertebrates and invertebrates such as honeybees can recognize and remember three and up to four objects, respectively.