He understands that you're the wagon boss.
5 seconds sound clip from the The Big Trail (1930) movie soundboard.
You can hear this line at 00:18:45 in the Blu-ray version of the movie.
Quote context
[...]
- Likely you two have met before.
- Nah.
- Coleman's gonna scout for the train.
- You understand, Flack, that he's to have final say in all matters dealing with the Indians.
- Yes? Well, who's got the final say about bossin' this bull train?
- He understands that you're the wagon boss.
- Yeah. Another thing, another thing...
- Am I supposed to be wet nurse to them woodenhead pilgrims a-crossin' the plains?
- The more that goes along, the better it is for them and you in case Indians jump ya.
- Make it clear to him that I'm wagon boss.
[...]