They were actually performing a dance known here as the Hokey Cokey, much loved towards the end of parties at which copious quantities of happy juice are consumed.
It starts
"You put your left arm in
You put your left arm out
in, out, in, out, shake it all about
You do the hokey cokey ............ (clasping hands across chest and rocking form side to side)
then you turn around,
that's what it's all about
subsequent verses use right arm, left leg, right leg then whole self.
Dates from the 1940s AFAIK.
Not dumb when you've had a skinful