They lack any meaningful design in comparison to other currencies, since all denominations stick to mainly black and white designs with slight hints of color as they've remained the same for a long time. Why won't USD switch to Polymer bills (it was first unveiled in Australia) like they've done in the UK or UAE for example.
You're supposed to add salt when you cook them, it helps bring out the flavor.
I've heard of money laundering, but this… 😁