The shadow your butt casts as you slowly squat down to drop a deuce.
Getting out of something right before getting shit on. Literally or metaphorically.
The last taste of freedom before the ominous shadow is above you.
Tom: "Jeremy look out! There is a crap shadow overhead and you are about to get shat on"
Jeremy: "oh shit!!!"
Tom: "Glad I carry this toilet paper around."