"Anything zombie-like, I'll just go for headshots anyway. You see in the movies how people shoot the torso and nothing happens? I'm not gonna let that be my demise. Untill I know otherwise, it's headshots so I don't leave room to underestimate.

A good start is to just observe. Are the zeds chasing people down or are they shambling around and grabbing hold of unlucky individuals?

Hearing... Throw different sized rocks at windows or trees or somthing, I dunno.
"

"I assume the tests are being conducted once a relatively fortified & safe location has been secured? Good theory behind testing the weak points, but pistols seem like a risky choice and would be the toughest to aim accurately enough to get the data you need. Why not one guy with a long range rifle?

In terms of other experiments that might be worth doing, I'd want to see what gets their attention & what doesn't;

-Fire a flare on the ground in front of a group of them. (Requires flare gun or launcher)
-Smash a window in the distance with something relatively quite(I.E. don't shoot it and add the sound of the shot to the stimulus).
-Light an object on fire & launch it near, but not directly at them
-Inflict a minor wound using a relatively quiet weapon(Requires bow/crossbow/airgun/slingshot/etc)

In each case, you'd be curious to see if they notice it and if it's more the sound or the visual that gets their attention. Also, you'd probably want to estimate how far away the furthest zombie to react was and see if you can account for what attracted it(the stimulus, or the other zombies). Also worth noting would be how long it holds their interest. I.E., how distractible might they be?

Other stuff you might test would be things like:
-Will they go after something like a raw slab of beef as aggresively as they go after people?
-Do they stand in place or wander when nothing is present to stimulate them?
-If they wander, do they automatically follow one another?"