Continuity mistake: In the beginning scene, the ruler of Argos is condemning his daughter and son to the sea with a group of guards present at the shore. While he is giving his speech, there is a brief moment when the whole group can be seen getting drenched by a wave crashing ashore, but in the very next moment of his speech - even up to the daughter's cast off - no one is wet.
Continuity mistake: When they are fighting the giant scorpions, there are three distinct scorpions fighting. Each of the remaining men faces a scorpion 1 on 1. One of the men dies fighting, and thats the last we see of that scorpion. Thello kills his scorpion, then throws Perseus his sword who then kills his scorpion. The third one just magically disappears.
Zeus: Perseus has won. My son has triumphed.
Hera: A fortunate young man.
Zeus: Fortune is ally to the brave.
Thetis: What a dangerous precedent. What if there more heroes like him? What if courage and imagination became everyday mortal qualities? What will become of us?
Zeus: We would no longer be needed. But, for the moment, there is sufficient cowardice, sloth and mendacity down there on Earth to last forever.