Reference for Niddah 141:29

אינה מטמאה משום כתם מפני שנעקר משמתה

IT CONVEYS NO UNCLEANNESS BY OVERSHADOWING.<span class="x" onmousemove="('comment',' Only a corpse or the prescribed minimum of a part of it conveys uncleanness in this manner. ');">²⁵</span>

Jastrow