dog observes food -
food is eaten -
state is changed -
state processed by dog -
not only is this tangible proof of the observation abilities of the dog but it is also evidence of higher learning. The output is the absence of the input. The dog is not merely commenting abstractly on the observation but materially altering it's existence. This also neatly bypasses the "translation problem" whereby no external observer can be sure that you have read a student's exam paper simply by noting that you put a tick at the bottom. If you were to eat that exam paper then the ambiguity would dissolve.