Scared Screenless

In case you missed it: The Professor acquires a teardrop tattoo while in jail.

Zoidberg's "two cans and a string" would never have interfaced with the telephones. The former work due to vibration carried along a taut string, while the latter function on wiring carrying electricity. The string would not carry electricity, and the wires would not carry vibrations (especially over the vast distances that also involve a gap in wiring).