Why does 'top' show three roslaunch processes?

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Whenever I use roslaunch to launch a launchfile (ha :)), the output of top (or htop) shows three roslaunch processes. One that is the parent of all nodes, and two more that have no children.

I could probably try to read the source of roslaunch, but does anyone here have any idea what those extra two are doing there? I've never seen more than 2, so it does not seem related to the number of nodes in the graph.