PS: Electrified cradle hypothesis

Karen Anne Kolling adds a comment to the "what happened to the eggs" mystery discussed in today's earlier post:

The current flow would have been in microvolts, and it would have grounded out to the building to which the structure was attached, I believe. I can't see how there could have been a current flowing through an egg, even if it were touching one of the metal prongs.

It's been a long time since I've been in school, but I don't think anything is going to ground through what looks like concrete, which is a pretty poor conductor.