i've had an alt parked in what used to be the alterac mountains (and is now just 'that part of the hillsbrad foothills full of snow and ogres and yeti') for a while now, looking for the elusive snowshoe hare. which is completely different than the snowshoe rabbit. even though they are identical. one you buy from a dwarf kid, the other you freeze your troll toes off, standing in the snow for weeks.
anyway. a few nights ago, i got all excited when two popped up on my minimap detector. i figured i'd catch one, then put out a realid message that i was looking at one in case anyone wanted to party up and crz in and catch it. (you know, i've never actually done that, so while i think that would work, i'm not 100% sure.) and then it all went wrong. first, i added a lowbie pet to my team so that i could damage him without killing him in one shot. but the pet i added (level 10 lil' deathwing) was still too high, and its first attack knocked the hare down to about 45%. uh oh. nothing to do at that point but hit it again, and of course that killed it. so I hurry up and kill its partner (a rat or something) and swap in a level 6 pet. and step forward to boldly to battle with the other hare, only it's not there anymore. crapdoodle.
eastern kingdoms safari. i wasn't sure, given what a hot mess that achievement is - there are six pets it shows me as still missing, four of which are actually sold by vendors (three dragonhawks and the cockatiel), as well as the crimson moth and wharf rat (which weren't in the pet journal when i caught them early in the expansion).
moral of the story, then, is be patient. some pets are pretty hard to find, and have really long respawn timers, but they do exist. use wowhead or the resource of your choice, figure out where they span, and park an alt there. check in every now and then to take a quick look. no sign of them, then move on to something else. sooner or later, you'll get lucky. and i'll be telling myself this as i hunt for the never-seen-by-human-eyes minfernal....