Continuity mistake: A sniper pops out of the hatch in the truck right when Batman knocks him, which makes him fall backwards. A shot later, the sniper is suddenly upright again.
Continuity mistake: After the guys are spotted in Siberia, the amount of snow under the shovel suddenly increases between shots.
Continuity mistake: When the guys arrive in Siberia, Flash knocks down a shovel which faces downwards. A shot later it's facing upwards.
Continuity mistake: The spider-web hanging from Batman's right side desk lamp, where Old-Barry types, disappears and reappears randomly between shots.
Continuity mistake: When Zod stabs Kara, she collapses, her cape lying sideways. Watch before she lowers her leg, and you'll notice there's no cape underneath her. A shot later, the cape lies under her body, down along her legs.
Continuity mistake: When Flash-2 finds Kara semi-dead, her head is pointing upwards. A shot later, it's facing sideways.
Continuity mistake: When Zod's ship leaves with Kara unconscious on the floor, there's a strand of hair over her forehead. When Flash-2 arrives, it's gone.
Continuity mistake: When Bruce serves spaghetti, the cutlery next to him changes positions between shots all the time.
Continuity mistake: After Bruce crashes against a table filled with boxes and food, he is covered in boxes. A shot later, when he tries to stand up, he is on top of the boxes and the way the food is scattered is completely different.
Continuity mistake: Bruce uses both hands to pour spaghetti, but a shot later he is just using one, and now his left hand is resting on the table.
Continuity mistake: Bruce extends his arm and offers a spoonful of sauce to Barry. A second and a half later, his hand is empty, and we later find out that the spoon is inside the frying pan. Way too fast.
Continuity mistake: When Bruce explains time travel, the salt/pepper mills keep changing positions between shots.
Continuity mistake: Bruce puts the spaghetti on the mat to explain time travel in a 12 o'clock position. A shot later it's in a 9 o'clock position.
Continuity mistake: Bruce puts the cooking pot to the right of the red pan. A shot later, they have swapped sides.
Continuity mistake: When Barry arrives at work and talks to his boss, the furniture and people around change all the time. Sometimes there's a white column on the left; others, there's a shelf next to it; yet others it vanishes and there's a box and a coat rack. Also, the guy on the right is sitting closer or further away randomly, despite the angle on Barry and his boss being always the same.
Continuity mistake: Right after Wonder Woman takes off, the people on the bridge vanish.
Continuity mistake: When Wonder Woman saves Batman and the other guy, there are skid marks on the right side of the road. When she takes off, they disappear.
Continuity mistake: When Barry meets his mother at the supermarket, he wipes the tears off his right eye. Shot changes and he's wiping his left eye.
Continuity mistake: In Batman's lair, after Barry has been electrocuted, the blood on his nose and mouth suddenly vanishes.
Answer: Some possible reasons gleaned from the Internet: Filmmakers wanted a different vision of Supergirl to reflect a darker, grittier personality and to show her refugee-like experience. Her dark short hair symbolizes her harsher journey from her home world. Also, it gives her a more androgynous look, reflecting both her feminine and masculine traits. Adopting a radically different look for an established character also shakes up viewers' expectations and generates more publicity and interest in the film.
raywest ★