The "Métro" is a good place to draw even if the conditions are difficult. It's complicated to keep sketchbook and pen stable. Most of the times it's too crowded and people get on and off to quickly, when they stay on for a while they tend to move all the time. It's also difficult to avoid bad looks when they notice you stare too much. I see lots of interesting faces I would like to draw on the subway but most of the time it's an impossible mission. So, when I can't draw for any reason I imagine that my eye is a "laser" that replaces the crayon. I follow every detail of what I see with my invisible crayon which is an exellent way to "sketch" without matérial and without anyone nowing.