[akomtu]

I think they even play the same role. At least the prominent occult authors say that all these effects are nothing but electricity and magnetism (snake is a typical occult symbol for electricity). Levitating a frog by a magnet is legit magick, NMRI is high-end sorcery. Things that are considered magical are various magnetic effects that haven't been discovered (by science) yet, but are known to people who don't quite understand the underlying mechanism. But in each and every case it's the good old magnetism. I'd guess that these sigils are meants to shape a magnetic stream produced by something else, and when properly shaped it tends to capture a "fish" of some kind. As for why the low type occultists use blood to fill these sigils, it's because of its magnetic properties (if you live in medieval ages, getting access to a lab with ferrofluids and 100 Amp generators is pretty difficult).