A Quiet Place Part II reveals more about its central monsters than the original film, but is the boat scene indicative of a plot hole, contrivance, or a clue for future films to explore further? Late in the film's second act, Emmett (Cillian Murphy) and Regan (Millicent Simmonds) discover the monsters can't swim, but one follows them to the island aboard an unmoored boat. It's not abundantly clear what the monster was thinking, but after it reaches land, it attacks anything that makes sound, in typical A Quiet Place monster fashion. Some key data are missing for the audience to know with certainty, but it appears that the monster waited before leaving the boat and attacking the humans. The question is, why?
While journeying to an island community Regan believes holds the key to disseminating their monster-killing secret, she and Emmett are trapped on the docks by feral people - "the kind you don't save," according to Emmett. In their escape from sure cannibals, they attract nearby monsters, who wreak havoc on the dock folk. Some who flee to a boat are pursued by the creatures, one of whom falls into the water and drowns, demonstrating their newfound weakness. Seeing this, its companion stays on the boat, stranded and without any way to steer back to the docks. As Regan and Emmett leave the cannibals behind and sail to the island, the monster's boat floats aimlessly until currents eventually bring it ashore on the same island.
Later, after having rendezvoused with the island community and rested a night, Emmett discovers the ship and hears the monster moving within. Soon after his horrific discovery, the monster chases after him and decimates the town. Here, a plot hole begins to form: why did it take Emmett approaching the boat - still from a considerable distance, and not abundantly loudly - for the monster to finally make its move? Given that they attack at any time of day in both this film and the original, it's unlikely it would have been resting; they don't appear to have such needs. Perhaps it didn't know it had landed until it heard Emmett, but it still ought to have been roused by the crashing of waves or the impact of the boat into the rocky shoreline.
It's possible the boat had very recently arrived upon Emmett's discovery of it, that both the sounds of landfall and of Emmett simultaneously coaxed the monster out of its vessel and into the town. This quickly explains away the plot hole, but is nonetheless contrived. For better or worse, A Quiet Place Part II employs several contrivances to maintain its high concept adventure: Emmett's shoes, Marcus's recovery, Evelyn's sidelining—the list goes on. While they don't detract as much as would straight-up plot holes, they do begin to call attention to the tenuousness of the world building.
Or maybe there's a different explanation entirely - a clue to their intellect. Perhaps the monster deliberately waited to attack, demonstrating a kind of selective destruction indicative of intelligence that the creatures are thus far not known to possess. Maybe it waited until it could be sure there were targets at play; having just watched one of its fellow aliens drown while attacking humans, it might have been reticent to attack before knowing the coast was clear. Going further, if the monsters are capable of reasoning in this manner, it's possible the creature helped determine the boat's destination, steering in the direction of breaking waves or townsfolk. This possibility sets up a third (or spinoff) A Quiet Place film that would explore the monsters' origins and motivations in greater depth.
Whichever explanation is most correct, and whatever direction John Krasinski and company take the franchise in future installments, A Quiet Place Part II remains a solid follow-up to a phenomenal franchise-starter. While there may be a few plot holes here and there, the wise filmmakers in control of this IP have proven themselves capable of approaching these not as flaws, but as opportunities to build upon. There's every chance the beat in which the monster waits before leaving the boat to attack is one such opportunity that subsequent films will utilize.