Continuity mistake: In the scene after The Celt defeats the big Thracian in a fight at the slaves' "new home", Master Graecus comes to get Bellator's explanation about the fight. After Graecus leaves, Bellator says "I'll remember you, Celt." Before Bellator says that, The Celt's left collar is below his shoulder. Just after Bellator says that, the camera cuts to show The Celt and his left collar is now on his shoulder.
Picture added by Kang Oedin