Richard Cook of Tapanui asks :-
Why does egg yolk and faeces stick to most surfaces and fabrics better than your average glue?
Stan Simpson, a biochemist and retired director of the Wool Research Organisation of New Zealand, responded.
The question contains an exaggeration. Most "average glues" available today are virtually impossible to remove from compatible surfaces once hardened..A few water soluble ones respond to lengthy soaking.
The main question posed however is an alleged persistent adherence of faeces and egg yolk "to most surfaces and fabrics". I know of no study on this particular point but I would expect all plastic, waxy or gel-type materials that become well embedded into a fibre mass or pressed onto many surfaces will be hard to remove. Consider discarded chewing gum patches on pavements! A good soak and generous physical action clears most if not all solid adherents of biological origin.
There is another aspect of egg-yolk and faeces. Both contain yellow or brown coloured compounds potentially able to stain fabrics. Bilirubins in faeces and possibly carotene type compounds in egg yolk. Carotene is the conspicuous colourant of carrots. On prolonged contact colourants such as these could penetrate into the surface layers of fibres. The stains do leach out again in a wash cycle, and the cleansing of soiled baby napkins has been perfected millions of times in home laundries with the aid of a little bleaching agent. Sodium hypochlorite in common household bleaches makes short work of destroying many types of stains and, very conveniently for napkins, is a fine disinfectant as well.