Animals are machines. So are plants for that matter. Your premise of what a machine is is incorrect. Or at the very least you're forgetting that given the exact same stimuli, eg a ringing bell, the exact same respnse happens, eg salivating.

Because animals are highly complex machines, there are huge numbers of variables that can affect the response - did the dog just get fed? Is it dehydrated so can't muster saliva? Has there been another program instituted?

Think of the systems you work with and how many variables you have to work with. How could the results change with one intermittent connection on one circuit? Then scale that to millions of circuits each with dozens or more _ways_ it could "fray".

But all things being mostly equal, the dog salivates no matter who rings the bell. And the girl is attracted to a fancier car or more pleasant talk, or whatever.