You Don't Need a Weatherman to Know Which Way the Wind Blows,

(Eugene Volokh)

and "no witness with a degree in scatology was required, nor was scientific testing required to establish the fact the
substance was feces," at least on the facts of this particular case (State v. Landis (Iowa Ct. App. July 13, 2011)). Thanks to How Appealing for the pointer.

UPDATE: I neglected to blog this line from the opinion, but commenter "a clerk" reminded me:

[I]t would be a rare person who had no personal experience with feces.