It varies by the individual but I agree. My females are fastidious, clean, a little high strung but most of all enjoy mental stimulation. Most often I find my nails under an investigation after handling food or a nice smelling object, like freshly washed clothes. I can see how this behavior is a mix of their boldness, motherly instincts to maintain a clean nest, interest towards tastes and wanting to entertain themselves all in one. With older females it may be hard to break of them of their habits however it can be done. I don't suggest flipping them over if they are past a certain age as it may be taken as aggression. I simply wash my hands the best I can and nudge them away. Sometimes letting out a sharp squeak (IF the intentions of the females is really just curiosity) lets them know you aren't enjoying your manicure.