Robert Benchley wrote, directed and acted in many short satirical films. He revealed how to watch a game in a 1923 article from THE HUMORIST.
We will suppose that you have found two people playing chess
somewhere. They probably will neither hear nor see you as
you come upon them, so you can stand directly behind the one
who is defending the south goal without fear of detection.
At first you may think that they are both dead, but a
mirror held to the lips of the nearest contestant will
probably show moisture. Soon you will observe a slight
twitching of the eyelid or a moistening of the lips and
then, like a greatly retarded moving picture of a person
passing the salt, one of the players will lift a chessman
from one spot on the board and place it on another spot.
It would be best not to stand too close to the board at this
time, as you are likely to be trampled in the excitement.
The players may even forget themselves to the point of
shifting their feet or changing the hands on which they are
resting their foreheads. Almost anything is liable to happen.
When the commotion has died down a little, it will be safe
for you to walk round and stand behind the other player and
wait there for the next move. You will perhaps find it
difficult at first to keep your attention on the board. This
can be accomplished by means of several little optical tricks.
For instance, if you look at the black and white squares
on the board very hard for a very long time, they will
appear to jump about and change places. The black squares
will rise from the board about a quarter of an inch and
slightly overlap the white ones. Then, if you change focus
suddenly, the white squares will do the same thing to the
black ones.
And finally, after doing this until someone asks you what
you are looking cross-eyed for, if you will shut your eyes
tight, you will see an exact reproduction of the chess-board
done in pink and green, in your mind's eye. By this time,
the players will be almost ready for another move.
Source: Evans on Chess - Nov 24, 1995 from Chess Connection