When Kate tells Guy that it's time for his medicine, she's holding the tray in her hands. In the next shot it's gone, and it is nowhere to be seen when the three of them leave the crypt.
Position of Emily's head is changed between two shots when she is lying on the ground in front of the grave.
In the cemetery Emily picks up a bunch of blue flowers twice.
In the tomb, Carrell refers to dynamite as a new invention. Since Poe wrote the story in 1844 and died in 1849, this would be impossible. Nobel did not invent dynamite until 1867.
When Guy is being examined for conclusion to whether he is dead or not, he can be clearly seen breathing, but he is still declared dead.
Sweeney can be seen breathing while being dead.
Emily can be seen breathing while being dead.
When about to show his guests the cup of poison, Guy refers to this as the coup de grace, but mispronounces it as "coup de gras" (as in "foie gras" or "Mardi Gras"). It is very unlikely that a well educated English grandee such as Guy would make such a mistake.