When McCoy walks into Zarabeth's outer chamber, he speaks but his lips do not move.
When Spock and McCoy return from the ice age, they're wearing heavy furs. When they reach the other side of the portal, the furs are gone.
"Mr. Atoz", is a library pun, "A to Z".
When the prosecutor visits Kirk in his cell a second time, between instantaneous camera cuts, Kirk's hands jump back and forth on the cell bars - sometimes he's holding adjacent bars, sometimes there are bars between the ones he's holding.