No idea what "fee-fi-fo-fum" is supposed to refer to

Calcium.

I dont think being on the bread line is useful when watching harrys farm https://www.youtube.com/watch?v=juXXt4ZHS-8&t=467s

or being in damp conditions.

https://en.wikipedia.org/wiki/Cladosporium#Health_effects

I can smell the mould in some brand new sliced bread and baps when its not out of date or anything visibly wrong with it.