Jewish feces covered by glass?

This is a halachic rule:

It is forbidden to say Krias Sh’ma, or other holy words, in the presence
of feces (Mechaber 76:3)

Unlike ervah, however, if it is covered by glass, it is permitted to say
Krias Sh’ma (Mechaber 76:1).

In what situation, would feces be covered by glass?