Correct!
They are connected together by string which must be pulled taught before speaking. Sound waves will travel down the taught string.
You can make a phone system similar to this using a length of
string and two clean yoghurt pots or empty baked bean tins.
Carefully make a small hole in the middle of the end of the pot or tin (use
a hammer and small nail and make sure there are no sharp edges to metal tins,
ask an adult to help), thread the string through and tie a knot big enough
not to pull through. With a friend pull the string taut, speak into the pot
and your friend should be able to hear what you say if they put the tin to
their ear.