Values Dissonance: A few issues that would be pretty uncomfortable in modern times are treated quite casually.
The book consistently uses "Gypsy" (which was not considered a slur back when it was written, unlike now) instead of the more appropriate "Roma".
The ethics of poaching, and hunting in general, is treated rather lightly (although Danny is horrified when he first finds out that such a nice man like this father would even consider poaching to be fun).
Mr Snoddy, who has been driven to drink by his wife's constant abuse, isn't given so much as a second thought. Then again, the story takes place from the point of view of 9 year old Danny, who wouldn't give it much, if any, thought. Okay, modern adult readers might not care either, sadly.