Rey and Finn are trying to retrieve Luke Sky walker’s light sabre from an enemy spaceship They sneak their way in to the armoury and discover over a hundred lighters piled up.
They don’t have much time as the guards could catch them any minute, and they have no idea which sabre is the one they’re looking for.
Quickly, Rey grabbed one saber, tossed it away, another one, then another, and until after a dozen sabres she holds onto one like she’s sure she’s found the one and proceed to run towards the exit.
Once they escape, Finn asks her how she was so sure earlier about that lightsaber being the one.
“It’s the only one that was… Lukewarm”, she replies.