Perhaps the cleverest monkey as yet studied was a performing chimpanzee
called Peter, which has been generally described by Dr. Lightner Witmer.
Peter could skate and cycle, thread needles and untie knots, smoke a
cigarette and string beads, screw in nails and unlock locks. But what
Peter was thinking about all the time it was hard to guess, and there is
very little evidence to suggest that his rapid power of putting two and
two together ever rose above a sort of concrete mental experimenting,
which Dr. Romanes used to call perceptual inference. Without supposing
that there are hard-and-fast boundary lines, we cannot avoid the general
conclusion that, while monkeys are often intelligent, they seldom, if
ever, show even hints of reason, i.e. of working or playing with general
ideas. That remains Man's prerogative.