Why that ?

[Sam Flynn]

I'm not entirely sure that someone still pumping adrenaline, who can revel in the blood and guts of a woman he's just slit open in a public place where he could have been surprised at any second, is going to be overly sickened or terrified by a bit of her poo on him

A "bit of poo", Caz? Eddowes' viscera were "smeared over" with it. The stuff was more than likely wedged between his fingers.

Besides, even the most extreme amongst us can exhibit distaste, or even sensitivity, when one might least expect it. Not that it takes much of a leap of faith to envisage a mutilating killer feeling disgust at finding someone else's whoopsy all over his hand.

I hear that it can even excite some men

"Scat the Ripper"...?