Revealing mistake: At the beginning when the ruler is making his speech, you can see his modern day fillings in his upper molars.
Revealing mistake: During the scene when Argos is being destroyed, a citizen falls backward due to the rushing waves and you can see a pair of black running shorts with white trim under his tunic.
Revealing mistake: When Calibos is speaking to Thetis' statue, as he screams "I demand justice", you can see the left horn on his head wiggling around, revealing a flimsy prop.
Revealing mistake: When the ruler of Argos is cursing his daughter prior to setting her adrift, we are treated to a couple of close ups where his modern dental fillings are beautifully displayed.
Answer: To me, it just looks like the way the prop catches the light as the actor lifts it up, and then higher up, the angle of the prop isn't catching the light in the same way.
Bishop73