Continuity mistake: The bullets that Leary removes from the keychain at the banquet are in a different position than they were when he put them in.
Suggested correction: We see him put the bullets in the rabbit's foot at least a day before the assassination attempt. Plenty of time for him to open the keychain simply to check and make sure he is fully prepared. Which does fall in line with his meticulous nature.
Character mistake: During the "heart attack prank" just before the paramedics get to Frank, Eastwood mistakenly opens his eye before the paramedics wake him.
Suggested correction: It's quite possible that Frank was awakened by the commotion of the EMTs rushing in.