When Gregorio and Ingrid escape and encounter the hallway with the floor of falling puzzle pieces, the pieces fall into a deep hole. But after Gregorio peels his face from the Plexiglas, you can see that the puzzle pieces are on top of the Plexiglas, not underneath it.
Just before the kids meet Machete, the cab drives away, and we hear the sound of it speeding into the distance. But the car is reflected in a nearby window and it can be seen that it just drove ten feet away to get out of the shot.
Across the road from the gadget shop, an old style black and white Irish signpost with Leopardstown (a suburb of Dublin) and the Gaelic translation written above (a feature of all Irish road signs) above is visible. The Irish-Gaelic reads "Baile an Liopaird" (Irish for "Town of the Leopard"), but the correct name is actually "Baile na Lobhar" ("Town of the Lepers" - hence originally Leperstown), which comes from a leper colony that was originally in the area.
As Ingrid agonizes over whether or not to proceed with her wedding, she knocks the head off an ice swan sculpture. She replaces it at an odd angle. A moment later the swan head is perfectly straight again.