Dirt under the nails is read as the traces of hard work, or as something unpleasant you have touched and cannot quite wash away. Context decides between honest labour and lingering guilt.
Has this come up in your dreams before? What was going on in your life then?
My Cosmic Code has a private dream journal. Write a dream down and the app picks out the symbols in it, shows what dream books say about them and, over time, which words recur across your entries. The journal is stored on your device only.