sketching on the train

I have had several London trips recently, and I have been furtively sketching other passengers. Trying to do it without them noticing!
I have been enjoying the graphitint pencil, and using a water brush to wash over the lines and bring in sone tone and soft shadow.
I also love the wobbly line that the motion of the train gives. I think it adds some life to the drawing.
I want to keep travelling now..it's becoming addictive!