Last night at my table, my party faced a goblin village. We pretty well know the goblin stat block contains the Nimble Escape trait. But still our DM never ever showed us that any goblin disengaged and since we had no visual clue, we thought the goblin were opportunity-attackable. Yet we could never land any opportunity attack on the goblin horde despite several uses of Dissonant Whispers (mostly on goblin bosses since they're the only ones with a bit of HP).
So can the DM use goblins' disengage bonus actions without clue and make all the goblins virtually immune to opportunity attacks, or should it be made obvious to players that goblins use their disengage bonus actions?