So Matt feels hideously guilty about the events in S2, and there's a lot of talking and reconciliation and apologies. But Matt thinks that he needs to be punished, too.

However, Foggy is 10000% not comfortable doing that. So they end up with Frank doing what needs to be done to his choirboy, with a cane or a whip or any number of things, and Foggy Nelson watching in abject...well, feelings.