A great portrait painter of the 17 century the Dutch painter Gerard ter Borch was known for depicting the rich and cultured people of his era but he also was a master painting the quotidian and rude people doing their activities.Here the boy, perhaps the son's painter Mozes, is picking fleas from his dog in total concentration. There are some books that may allude to the diligence that he dedicate to this activity.
According to WIkipedia:
" His figures are well drawn and expressive in attitude; his colouring is clear and rich, but his best skill lies in his unequalled rendering of texture in draperies, which is seen to advantage in such pictures as The Letter and in The Gallant Conversation engraved by Wille – which exists in various repetitions at Berlin and Amsterdam, and in the Bridgewater Gallery."
This is interesting when we have this documents of daily life from other epochs. (click to enlarge. this is a very dark image)