Certainly since Scripture related nothing about the places which we said were set apart for the excrement of the animals, but tradition preserves some things, it will appear opportune that silence has been maintained on this about which reason may sufficiently teach of its importance. And because it could less worthily be fitted to a spiritual meaning, rightly, therefore, Scripture, which rather fits its narratives to allegorical meanings, was silent about this. (Genesis Homily 2; trans. Ronald E. Heine, p. 75).
The last sentence gives Origen's operating assumption about scripture: that it is made to be allegorized; anything that might fit a literal interpretation but not an allegorical one has been omitted - though he admits there are some traditions that try to close the gap.
Ultimately, however, you just can't spiritualize crap.