While it’s well known that coils have strong inductances, you may not realize that all non-coil signal lines, including straight lines, have some inductance. Moreover, mutual inductance can be a source of coupling between isolated signal lines. In fact, you should be aware that electromagnetic induction can occur not only between parallel signal lines on the same side of a printed circuit board (PC board or PCB), but also between signal lines that run parallel on opposite sides of the board.