I've tried to explain magic with science in some of my settings, and while I can get some things to work, there's a lot that just completely conflicts with known sciences so much you have no choice but to say "its magic!".

For example, how can you explain polymorphing/shapechanging spells/abilities with science? (or at least in such a way that allows complete reversal with no physical harm to the object) Like our much-loved Toad spell in PoTD...