Two terminal devices circuit puzzle

Hi
I came across the following puzzle which involves circuits and two
terminal devices but i think it's basically a mathematical puzzle. But
i am unable to understand it.
Puzzle:
In any circuit containing only "two terminal" devices we can always
find two "links" whose removal (not simultaneous)
still left all the components connected to each other by wires.
a hint was also given : consider an unplugged toaster as a valid
circuit in this puzzle.
I am unable to understand what is a circuit with "two terminal"
devices and what are "links" in it.
Can anyone give an example of such a circuit in which the above
property holds.
I think this problem can be converted into graphs. But i dont know how
if it is possible?
Please help.