How does Aegis work?

[Heroshrine]

It says shields for overhealing. I search it up and it says +50% of the heal as shields. But it seems to only work with like one or two healing items. For example, I have the item that gives +100% healing. I have 3 meats. I kill some enemies, I get no shields. ??

[TrueEvil]

It doesn't work on regeneration. This rules out Fresh Meat, Cautious Slug, Titanic Knurl, and your normal HP recovery.

The healing needs to be in the form of the green numbers that show up on your character. Fungus, Monster Tooth, Desk Plant, Scythe, Seed, Woodsprite, Fruit, Strides of Heresy, Lepton Daisy, Medkit, and Corpsebloom (kind of).