When Johnny first appears, he, Rebecca and Benjo are all in fields close to the house that are covered in snow. Moments later as the doctor arrives, the snow has largely disappeared and is seen only in patches.
In the scene with rain where Rebecca's father and brothers come to the house following her being discovered with Johnny, it is pouring rain as they are standing outside, yet Rebecca is relatively dry moments later in the barn.
Rebecca is seen helping ewes in labor and Johnny is seen with a lamb during the same scene. However, despite seeing the herd a number of times after that, no lambs are ever seen again.
In the lambing scene, when Johnny first sees the lamb in the straw, the lamb wet and slimy. A moment later, while still covered in straw, it is dry and fluffy.
The bullet that the doctor extracts from Johnny Gault is a modern style - a semi-wadcutter. Most pistol bullets in the 1880s were round nose style.
When Woodrow is laying on the ground after being thrown from his horse and Johnny is holding his own rifle on him, a con trail can be seen in the sky over Johnny's shoulder