When Clint and Kate arrive at Clint's home on Christmas Day, when seen from outside the house has a storm door and an unadorned inside door, but from the inside there is no storm door and the inside door now has a wreath on it.
During the musical in the end credit scene, when the Avengers are standing next to each other on the bridge, Hawkeye is seen standing to the right of Steve Rogers and to the left of Black Widow, when the scene zooms in on the Hulk, Hawkeye is standing next to him in Thor's place. When the shot zooms out again Thor and Hawkeye are back in their original places.
In the finale, Yelena Delova tosses her stick on the ground and draws her gun at Clint. Just after he whistles, a call and response that she did with Natasha back when they were kids in Ohio, it cutbacks back to Yelena holding the stick again instead of the gun, and when it cuts back to Clint she is putting the gun in its holster.
When Kate breaks the window at FAO Schwartz and fires at the Tracksuit Mafia, a safety harness is visible around her waist above her archery belt. The harness is gone when she prepares to fire at the Christmas tree.
The owl in the tree was a Saw Whet owl. They do not make a deep hooting sound, they make a faster, high pitched toot.
As Kate quick-steps into the elevator with Yelena, the safety sensor should have detected her entry and re-opened the doors, instead of continuing to close.
Not all elevators have this feature. And, more often than not, it doesn't work as expected.
Not all elevators have this feature. And, more often than not, it doesn't work as expected.
When the Tahoe stops at the Barton homestead, only the driver is visible through the windows, despite Kate and Lucky being in the car as well.