Earlier quoted context omitted.
> "Don't look a gift horse in the mouth" The winners apparently write both the history and the idioms. The Trojans would have done well to look a gift horse in the mouth. A wooden horse can be full of physical soldiers and a digital horse with legal ones.
Looking at a real horse's teeth shows how worn down they are over age. Looking at a horses teeth is to check its age. The idiom could be modernized to: 'dont check the odometer of a gift car'
In the case of other "gifts" the value can be negative. The trojan horse, software, and blankets from Lord Jeffery Amherst all need careful examination.