Continuity mistake: While Finn, Rey, and BB-8 are hiding in the maintenance bay to unfix the poisonous gas, when Finn lifts the floor's slotted deck plate and pokes his head out there are specific grooves at the edge on top of the plate, but no grooves underneath at the edge. The problem occurs when Chewie lifts the deck plate, and those grooves should be on the side facing him (the top side), but instead they're facing out. Then when Han tells Finn "that thing" can understand him, the grooves are gone - the top side of the deck plate is properly facing out.
Picture added by Super Grover
To submit a picture, just click the edit icon under the relevant entry, then choose 'add a picture'. Thanks!
All images remain the copyright of their original owners - these low resolution images are simply individual frames used to demonstrate the entry.