This guy had been in hospital for a long time, during which he lost a lot of weight. When he returned to his garden, his dog didn't recognise the 'stranger' and barked at him. Once the dog had plucked up the courage to sniff the intruder in his territory though, things suddenly changed very quickly ;-)
I saw a programme (part of a dog behaviour series, i think) where the master of the house had suffered a stroke. His once faithful dog did not recognise him (because of the way he walked and sounded) and would constantly bark and sometimes attack him, if he so much as moved. The 'specialist' suggested one or two things the couple would do with the gradual result that master and dog are once again best friends.
I think that, as animals that use our eyesight to identify people, we usually fail to remember that our furry friends are different.
I remember a video of Christian the Lion and his reunion with his humans, the Lion stalked the two of the guys initially until he was nearer and saw and smelled them.
Cats can be unable to see a morsel of food put down in front of them but then their ears and eyes pick up a mouse moving some distance off.
Polis Dugs are really fascinating animals too - especially the hunky big hairy German ones.
Tried to find the video Chris. Thought it was 'Dogs Behaving Badly' (Channel 5), but none of the episode synopsis tally. If i do remember where i saw it - i'll probably wake from a deep sleep at silly o'clock, sit bolt upright and shout out the name of the programme - i'll post it.