River doesn't bother to give Duo a smug look in return, but there might be the ghost of one on her face for a second anyway. Worked, didn't it?

Also, ooh, somebody dropped a gun. River takes the chance to dart out and grab it.

Back behind the crate, she ejects the clip long enough to check how full it is -- three-quarters or so, fortunately -- and slap it back into place. Now random scavenged projectiles aren't her only distance weapon.