r tells his audience that he is about to do a certain thing, for
example, take a number of animals out of a small box which is incapable
of holding them. The hearers, intent on what has been said, vividly
represent to themselves the action described. And in this way their
attention becomes bribed, so to speak, beforehand, and fails to notice
the inconspicuous movements which would at once clear up the mystery.
Similarly with respect to the illusions which overtake people at
spiritualist _seances_. The intensity of the expectation of a particular
kind of object excludes calm attention to what really happens, and the
slightest impressions which answer to signs of the object anticipated
are instantly seized by the mind and worked up into illusory
perceptions.

It is to be noted that even when the impression cannot be made to tally
exactly with the expectation, the force of the latter often effects a
grotesque confusion of the perception. If, for example, a man goes into
a familiar room in the dark in order to fetch something, and for a
moment forgets the particular door by which he has entered, his definite
expectation of finding things in a certain order may blend with the
order of impressions experienced, producing for the moment a most
comical illusion as to the actual state of things.

When the degree of expectation is unusually great, it may suffice to
produce something like the counterfeit of a real sensation. This happens
when the present circumstances are powerfully suggestive of an immediate
event. The effect is all the more powerful, moreover, in those cases
where the object or event expected is interesting or exciting, since
here the mental image gains in vividness through the emotional
excitement attending it. Thus, if I am watching a train off and know
from all the signs that it is just about to start, I easily delude
myself into the conviction that it has begun to start, when it is
really still.[53] An intense degree of expectation may, in such cases,
produce something indistinguishable from an actual sensation. This
effect is seen in such common experiences as that the sight of food
makes the mouth of a hungry man water; that the appearance of a surgical
instrument produces a nascent sensation of pain; and that a threatening
movement, giving a vivid anticipation of tickling, begets a feeling
which closely approximates to the result of actual tickling.

One or two very striking instances of such imagined se