Mystery Solved. It was really very simple. One of the
Jerseys was butting her head up against the gate. She
would do it until the bungee cord popped off (we close
that particular gate with a bungee cord, don't ask me why-
it's just what we do.) Then she would wander into the yard,
followed by whoever was in her vicinity. Really it is fine
for them to eat in the yard. We have a quite big yard, and
we can always use help with keeping it cut, but the next
time we mow we need to watch out for the cow you know
whats.

I guess it wasn't really worthy of the spooky music, but I
was befuddled for a bit!