Emphasis appear. Someone else mentioned the same thing on Reddit when this video was posted there yesterday. I'll copy my reply to it:

> If you pay close attention to the background you see that it's looping. Near the end when they're about to enter the kitchen you see that the distance from the doorway to the wall is one, two meters at most (er... about 6 to 9 feet?), but then when they enter it you see a cupboard pass by 6 times before Gromit crashes, which basically means that the space has been stretched out six times.

> I think that just shows how much movie magic the scene has: space and time are stretched and squashed to meet the needs of the narrative, reality be damned! And unless you specifically look for, it you'll hardly notice because you're too caught up in the excitement.

Just like how you don't care that there's infinitely many train tracks in that box. It's basically The Rule Of Cool:

http://tvtropes.org/pmwiki/pmwiki.php/Main/RuleOfCool

... and a TARDIS of a train track box.

So that's how they fit curved track into it.