The violin made another appearance in second season ep. "Bad Blood" as well as in a "Dark Knight" fb (watch more closely next time). Also, in the third season ep. "Blind Faith" Nat mixes one of her god-awful concoctions for him (saying that he could chew on rusty nails for a year and not get as much iron) and, after tasting the drink, Nick comments that rusty nails would taste better.
Just so you know.