Are you more likely to get one experiment more than another? I've been zapping more of my pets and I seem to be getting certain experiments multiple times and other not at all.

this is bad luck on your part I think. I have a number of zapped Experiments and I didn't see any trends back when I was tracking it.

It could very well just be bad luck as Solsticesprite said, but I will admit that I felt like the same was happening to me when I was zapping a few months ago. Then again, it's entirely possible that it was just bad luck on my part to. :P

I'm convinced Euclid somehow knows which experiment pet you want and thus doesn't give it to you because he's a handsome jerk.

Same! lol. Eventually it got to the point where I had gotten all but about 5 or 6 of the experiments, one of which was the one I wanted.

i was recently zapping for a specific experiment and never got a duplicate the whole time, it was a new one every zap until i got the one i wanted. maybe i was just really lucky but i assumed it tried to skew towards experiments you hadn't gotten.