It moves the value of register (a CPU memory cell) rbx to register rax. It's not that important though.

Basically the comic shows that the CPU is happily chugging along, executing instructions when suddenly the keyboard sends an interrupt telling the CPU it must stop all work and listen to whatever it has to say.

That was how keyboards worked before USB (back when they used PS/2 or DIN connectors). With USB it's the other way around: the device gets polled X times per second to check if it has any data to send.

It's irrelevant to the humor, it's just an arbitrary x86 instruction. The point is that keyboard inputs (with a PS/2 keyboard) interrupt whatever the computer is doing

Though to answer your question, it moves the value from the rbx register to the rbx register

These are some assembly instructions that the computer is happily running with no keyboard input. The keyboard input is then coming in as an interrupt demanding immediate processing which is silencing the poor background bird process.