On the fiddle

There's no single confirmed source for this one. One theory ties it to naval life: a "fiddle" was a small raised rail around a mess-table at sea meant to stop plates and cutlery sliding off in rough weather, and sailors trying to fit more food onto their plate than the fiddle's edge should really allow gave rise to a general sense of "getting a bit extra you're not entitled to." Others link it simply to the older use of "fiddle" in thieves' slang to mean a small swindle or scam, recorded from the 1700s onward, independent of anything nautical. Both are plausible; neither is proven.