Maybe 'cuz you can get a blister opening them???

Well, that's what I thought too, maybe. Seems too simple though...

I vote for EMT shears.
Mangle a few blister packs then return the item with the pack destroyed. I do not care anymore if I ruin the pack when I need to return something.

I use my electrician's scissors to open clamshell packs.

I destroyed the hinge of a pair of inexpensive trauma shears working on blister packs. Other than a sharp knife, maybe a band saw?

IF they have the hole thing at the top, that they hang them from in teh stores, i usually am able to actually put one finger inside and rip it. Works pretty well, unless it doesn't have a hole, then i use my kitchen shears.

I think they call them blister packs because if you see them without the contents in them they look could like blisters, the soft plastic on cardboard especially so. Just guessing.

Works for me..

I reckon they are called blister packs because of the way they are put together. The plastic is heated until it is malleable, then is pressure formed over the item it is to contain along with the carboard backing vis-a-vis some sort of die forming machine, then the edge is welded together to seal it up. Since the plastic is a smooth sheet before it is heated and applied, it is much like forming a blister over the contents.

Very good. Very good. Thank you both. The mystery is thereby solved.