Building the nest requires sealing it. They don't coat it with dung unless they smell wasps nearby.
"However, if a small lizard or mouse, for example, finds its way into the hive and dies there, bees may be unable to carry it out through the hive entrance. In that case, they would attempt instead to seal the carcass in propolis, essentially mummifying it and making it odorless and harmless."
Example picture: https://www.researchgate.net/figure/A-mouse-skull-that-was-e...