It is recommended to lick one's fingers and wipe the bowl, and to eat a piece of food that is dropped after removing any dirt on it. It is disliked to wipe one's hand before licking it, because of the possibility that the blessing of the food may be in that remaining part. The Sunnah is to eat with three fingers

وَحَدَّثَنَاهُ إِسْحَاقُ بْنُ إِبْرَاهِيمَ، أَخْبَرَنَا أَبُو دَاوُدَ الْحَفَرِيُّ، ح وَحَدَّثَنِيهِ مُحَمَّدُ بْنُ، رَافِعٍ حَدَّثَنَا عَبْدُ الرَّزَّاقِ، كِلاَهُمَا عَنْ سُفْيَانَ، بِهَذَا الإِسْنَادِ ‏.‏ مِثْلَهُ ‏.‏ وَفِي حَدِيثِهِمَا ‏ "‏ وَلاَ يَمْسَحْ يَدَهُ بِالْمِنْدِيلِ حَتَّى يَلْعَقَهَا أَوْ يُلْعِقَهَا ‏"‏ ‏.‏ وَمَا بَعْدَهُ ‏.‏