Q How did Pachycephalosaurus use its hard head in territorial disputes?

It was previously believed that Pachycephalosaurus slammed their heads together in combat.
However, we now know that their neck bones were relatively thin and not robust enough to withstand the extreme shock of hard, head-to-head collisions.
As a result, it is currently thought that they settled territorial disputes through visual displays, showing off and comparing the impressiveness of their heads instead.