How did viruses photosynthesize when they're literally smaller than the cell structures used for photosynthesis?
The wizard did it, poh. When you're dealing with young-earth creationism and flood geology, that's literally the entire answer. God did it, real geology can get buggered, etc., etc.
Which can be consistent with the narrative, of course. God is supposed to be all-powerful, so yeah... Maybe he did modify the animals and bacteria to eat each other, and maybe he waited until after the great flood. And maybe the ark was like the TARDIS, bigger on the inside.
The question becomes not "How is that possible?" but "Why would He do it that way?". Does it make any sense for God to have a human build a boat to hold samples of every animal, when He could simply allow them to breathe water in the interim? Possibly so, if he wanted to test Noah's family or just do something cool. More problematic are things like Jesus's sacrifice, or Hell, or a hundred other things which I have trouble reconciling with the rest of the book. Though discussion has helped me figure out a few!
Which is one reason why I get annoyed by "God works in mysterious ways". An entity that can do anything, but does unpredictable things with no rhyme or reason, is boring to theorize about. God killing or ordering the rape of people in the Old Testament: makes sense after a while, as his character is established and outright stated to be jealous and wrathful. God then turning around and making a sacrifice of himself, to himself, with no lasting consequences except that he manages to forgive all of humanity for something two humans did? Doesn't really fit with God's established nature, or any sort of internal logic.
FAKEDIT: Oh dear many ninjas. What do you call a group of ninjas even? Is there a specific term?
I'd say a "massacre". As everyone knows, ninjas are incredibly fragile and inept in groups, yet more confident and violent than ever. An unfortunate combination, for them.