When Che is outlining his conditions to the UN, one of the cutaways shows some soldiers crossing a muddy river. During the scene, a crew member in contemporary clothing can be seen standing on a grassy bank to the left of the frame.
When the guerrilleros are in the Sierra Maestra, we can hear the coqui (Eleutherodactylus coqui) singing in the night. However, this small frog is endemic to Puerto Rico and the Virgin Islands, thus not possible to be heard in Cuba.
The film leads the viewer to believe that Guevara was hired as a mercenary and a combatant. In actuality, he was hired as a medic. It wasn't until he was seen running into battles that he became a combatant.