B follows, or rather climbs and jumps around in parallel, usually taking different roads through the more literal concrete jungle, sometimes close by and sometimes a little ways off. There's plenty of room for both of them to create their own obstacle courses in here, whatever best suits them, and B keeps mostly out of Marc's way since he doesn't think they're friendly enough yet for a teasing competition or amiable jeering.

Neither of them can be hurt here more than bruises, the Enclosure setting is set too low for that, but he keeps an eye on Marc just in case as well-- and also to watch how he moves. He notes what risks he does take, whether any tension comes down from the activity, and when he looks like he might be ready to stop. Or when his body looks like it might be ready to stop, because he knows the tendency to push yourself too much, especially after some stressful days.