You overlook function. That version of the knot becomes jammed when seriously ring loaded.
If the victim will try to stand on her feet by pulling those curtains, while she is being stabbed,
then yes, we will have a crime scene with jammed Zeppelin loops all over the place
--but I believe that would be the last thing the audience would pay attention to ! 
What is the real problem is that, when the tails of this Zeppelin loop will be loaded,
they will both point downwards ...
Actually, if the point is to build a series of rings with the
eye knot eyes ring-loaded, then one should be musing
about tying the
reverse zeppelin knot --which, ring-loaded,
is exactly the
Z. ! --ditto for various other such knots.
Otherwise, one might point out that the
carrick bend, Ashley's
bend (#1452), & #1408 all have tails exiting the knot together
and so make for attractive eyeknots in some circumstances
(though none of these is TIB (Tyable Inthe Bight / sans ends)).
Now, as a practical matter for something like hanging a shower
curtain, I can imagine that one would adopt a rigging technique
akin to making a net, working from one side to the other,
casting a bight around the rod and through the curtain ring,
and then reeving the working end (of material bunched around
a netting needle) to seal the deal, and move to the next point
--the working/sizing being the prime concern, not strength or
jamming or fancy with some particular knot that has no business
here. (I've not explored such a working-like-netting construction.)
--dl*
====
