There is something quintessentially Russian about the ticket barriers in the metro. Some, it is true, consist of plexiglass gates that, in quite a sane and civilized manner, simply fold open when you tap your metro card. However, the majority of barriers work in a different manner all together.
These gateways are deceptively
empty and open looking, but if you tap your card wrong, move too slowly,
are out of credit, or fail to tap a card at all, a tinkling alarm sounds and a barrier crashes out of either side of the gateway in a vicious attempt to
trap you. This hurts. A lot. To the point of leaving bruises. In fact,
the barrier guards rarely bother pursuing people who have set the alarm
off, probably assuming that this painful attack on the person's legs and
sensitive bits was repayment enough for not properly paying the
forty ruble metro fare.
The upshot is that a necessary step for entering most metro stations is, quite literally,
paying a machine to not punch you in the cunt.