They are actually saying "salt and vinegar?" but if you're not an experienced chip shop go-er you will have no idea what they're on about.
In-experienced Chip shop go-er: "excuse me?"
Chip shop worker: "Sore finger?"
In-experienced Chip shop go-er: (Sometimes they figure it out, in other cases they just nod politely to avoid embarrasment and On rare ocassions actually comment on how they haven't got a sore finger)