from 0 Ohm (wonder what such a resistance exists..
These are called zero ohm links and are used quite a lot by professional engineers. Mainly when laying out a PCB they often have alternatives they would like to try, like the choice between an internal oscillator and internal. They lay it out and then put zero ohm links round it so they can swap between one configuration and another just by removing and placing these links.
To the others:-
I thought there was a 30 mA limit on Arduino I/O pins?
We are talking about inputs not outputs here.
5v/10k ohm = 0.5 miliamps
Yes but that is only the current going through the button when pressed, the arduio input pin takes some but that is very tiny.