As a rat obsessed rat owner. Picky eater isn't quite right - Rats practice food neophobia and have a (oddly) highly developed vomeronasal organ, their olfactory receptors are the highest density among animals, and their olfactory bulb is significant for an animal of their size and strength. It's thought the food neophobia simply comes from centuries of us trying to kill them.
https://pubmed.ncbi.nlm.nih.gov/1840504/ (https://www.cell.com/cell/pdf/0092-8674(91)90418-X.pdf)