Lyric discussion by mozza_fan 

Cover art for 4 lyrics by Aphex Twin

The little 'Richard, yup' bit I always thought acted as a sort of little reminder to himself to bring the song back to its basis. If you notice, it comes in right when the tune's drifting away from the beat and main melody and it's acts as a little reminder not to get too carried away and ambient! Richard, yeah? And that amazing energetic beat kicks back in. I don't think it's his mum, it sounds like a man's voice, it's probably just random sampling from his studio tapes or something.