Great show but yea I am troubled over the same thing.
Watching it with my daughter. Shes a horror movie nut. Makes for good family time for us. With my RL Nickname being "Gomez" would this really surprise anyone? LOL
Anywho. Watching the show raises a couple of questions about zombies and the show with us.
1 Why arent animals like rats or other animals that are often used for medical testing before humans also turning into zombies?
2 since zombies are dead. How long before they die or fall apart through natural decomposition?
3 How long before on the show to they take a zombie as a sort of a pet?
Yeah, I noted the use of the rock on the glass doors and thought that an unnecessary plot hole; I've read some of the comic book series, and that was not in there IIRC. These zombies are faster than what was depicted in the comic books, too. There were a couple other plot holes I've noticed, but they escape right now. Regarding your other questions...
1) Note that viruses only rarely jump species, so this is not surprising that they haven't run into other species who've been infected. It's one of the reasons medical science has such problems curing viruses; research on animals is of limited value. One example of a cross-species virus is ebola (certain simians and humans). Another is leprosey, which in all the animal kingdom only seems to affect humans and armadillos.
2) This is a good question. If you consider Max Brook's to be an authority (author of "The Zombie Survival Guide" and "World War Z: An Oral History of the Zombie War"), his version of events writes that the zombie virus makes the zombified flesh toxic to other living creatures, such as the bacteria that tends to break down dead flesh. This tends to slow the decomposition process down to a crawl.
3) Wait for an upcoming episode...