Operation: Silent Night - S4-E10
Other mistake: The three friends mistake Higgins' footprints in the sand for a pirate's. They find him and they have their explanation; Higgins is carrying a cane and some palm leaves; dragging the palm leaves, he involuntarily erases the prints of his foot, while the cane leaves a circular print akin a wooden leg's. That makes no sense, because as it is shown, Higgins is holding the cane in his right hand, and dragging the palms with his left; he'd wipe the prints of his left foot, if anything. And yet when Rick pointed at the prints, it was obviously a left footprint. (00:18:20)
Operation: Silent Night - S4-E10
Other mistake: Higgins ask for the hacksaw from TC's toolbox. In 30 seconds sharp (no pauses in the dialogue), Rick brings it to him. So the wrecked airplane and the chopper are 10 seconds apart, in a thick forest. That's quite a bit uncanny. (00:24:15 - 00:24:45)