Arduino reset serial issue

Today's lesson: experimenting with some serial stuff (*) I saw Arduino Mega rebooting... Welcome to the Infamous Reset Issue. Gotta find a "120 ohm" resistor (that is: compose some resistors to get a value between 110 and 124 ohm).

More info on the Arduino Playground.

(*) it only was Serial3.begin(115200); Serial3.print("test");