what is the difference between 條 and 匹? In the context of "classifier for long thing objects" how do 條 and 匹
differ?
When used as measure word, 匹 always has very specific and narrow matches with it


  一匹马、一匹骡子、一匹狼、一匹布、一匹绸子


Above is pretty much all you would see with 匹 as a measure word.

For 条，except for dog, it always refer to animals that are long, thin and with no legs, like


  一条蛇、一条鱼


Also, it refers to general long objects like


  一条绳子、一条河、一条腿、一条烟（lots of boxes of ciggrets purchased together）


Moreover, 条 could refer to human body related concepts


  我们几个是一条心、一条人命