modifying talking Thomas trains

Thanks Nigel. You lost me there... but thankfully I have the interwebs. I opened one up and it looks like they put resistors on there, the part I don’t get is there is a capacitor too??? I know these type of motors are usually rated for 3-6 volts so I’m not worried about giving them too much juice. I was hoping that there would be just the resistors and I could swap them out so the motor gets another volt or so, but the capacitor confuses me