I'd forgotten about the photo, Sean! Interesting and insightful theory about it! I actually just finished reading the book a couple of days ago. It answers my original question about the acid (I won't give it away here) and presents a lot of plot/character details that, of course, did not make...
Yes, the movies were very similar. I found the pool scene in both to be very effective and creepy, but the hospital wall climbing scene was much better in the first. In the second one, it looked like they'd hired a stunt person to clumsily climb; in the first one (as I recall) Abby shimmies...
Why did Abby's father-figure/aide even carry acid around with him? This was in both movies and it was unclear to me why he had it with him at all. Was it just his version of a cyanide pill in case he was caught? If so, seems like there would have been better alternatives. Any theories?