You should keep a better eye on him if he's to be king one day.
5 seconds sound clip from the 300 movie soundboard.
You can hear this line at 00:55:23 in the Blu-ray version of the movie.
Quote context
[...]
- Think of the two days as a gift.
- It's no secret Theron wants what you control.
- It's his voice you must silence. Make him your ally and you will have your victory.
- Thank you. You are wise as you are kind.
- You should keep a better eye on him if he's to be king one day.
- Be unfortunate if anything were to happen to him. Or to his beautiful mother.
- No! Ahh!
- Our Greek comrades are begging for a crack at the Persians, sire.
- Good. I've got something I think they can handle.
- Tell Daxos that I want him and 20 of his best eager, sober and ready for the next charge.
[...]