Funimation has a contest asking "Go to the FUNimation.com forums and tell us (in 100 - 400 words) how you would find out if your hypothetical crush was a zombie. Without letting him/her know and without potentially hurting him/her, of course." for the release on the "Is this a zombie?" DVDs.
Here's what I said:
I’d make her a lovely meat dinner but I won’t cook the meat and see if she notices the raw taste or the blood. If she did notice I’ll just say I forgot to cook that one and switch plates. After dinner we’ll sit by a fire. I give her a too hot chocolate and see if she feels pain in her hand. If she feels the pain I’ll be sorry, but if not I must continue to find out.
Later I’ll say “how about I play with your hair?” (I’ve heard girls do like that). If her hair starts to come off too easily it’ll be another point to that her body isn’t work to maintain itself. If the hair stays then it could just be good roots. Time now to give a foot massage. While she’s lying on her front or back where she isn’t looking at her feet I’ll start to break her toes. If she starts to feel the pain before the break I’ll stop and say I wasn’t use to such delicate feet. If she does feel the pain but hears the snap of the break I’ll say “I popped your toe” while knowing she isn’t what she want me to think.
That night I’ll pretend to sleep and sometimes see if she’s still awake at odd hours. She could have a sleeping disorder. If she doesn’t sleep any during the day then is shows that she don’t need sleep like a living person. She also may eat to act like a living human but does she use the toilet like normal person then she would be using any toilet paper. I’ll be sure to keep track of how much TP she uses if any.
I would also take her to a beach on a hot sunny day and after a few hours of tanning and play she still feels cold to the touch it’s help prove that her body isn’t pumping blood. We could also go swimming and see who can hold their breath the longest. If she is able to hold her breath for several minutes that could prove she doesn’t need oxygen.
There are many ways to test but really if the one you care about likes you and no one is getting eaten then what does it matter.
Here's a trailer for the anime and I'll be sure to give this a look over.