RH (18) [Avatar] Offline
#1
PDF page 101:
Then, in the constructor, you also subscribe to the
DeathWatch notifications for each of the actors you’re interested in.

As per the code example, this happens in the PreStart() override, not in the constructor:
protected override void PreStart()
{
  foreach(var actor in _watchedActors)
  {
    Context.Watch(actor);
  }
}