Edit: This bug has been officially fixed in the Hook, Line and Inker beta. You will no longer be dealt damage when hammering the Egg if you're wearing any piece Electrical Insulation clothing.
If you hammer a Moose/Goose egg but are wearing Electrical Insulation clothing, you are still dealt 10 damage per hammer, even though you are not being shocked.
Is that supposed to be the case?
Wear an Eyebrella or Raincoat. Hammer the Moose/Goose egg. Notice that even though you don't get shocked, you still lose 10 hp regardless.