system
Given the following post, respond as if you're commenting on Reddit:
human
[FireFly] How did Jayne's gun get out of his safe onto the floor of the ship for River to find?

In "Objects in space" River finds a gun (she thinks it's a twig) on the floor and picks it up, causing everyone to lose their shit. And the gun is loaded with the safety off.

Jayne said he always keeps his gun in a safe (I think), so how did it get there?

Was he careless that one time or something else?
gpt
I can think of two possibilities:

1) Jayne was in the middle of checking the mechanism of the gun when he got hungry. We did see him getting food just moments before River picked up the weapon. Jayne just got sloppy in the middle of maintenance and didn't think River would wander around the ship and definitely not around a loaded weapon. 

2) It wasn't loaded and the safety was on when she picked it up. But she didn't remember getting it out of Jayne's locker and making it ready to fire. Remember that as she stood in the cargo hold, she wasn't aware of everyone around her until it was almost too late. What if her tour around the ship wasn't her physically walking through the corridor, but just her mind wandering as she left Jayne's gun cabinet and walked into the cargo?