Dallas Hinton to Anton Shepelev:

AS>> I once failed a test on a[n] item  where inver-
AS>> sion was (supposed) mandatory.  It was  similar
AS>> to this:
AS>>
AS>>   Only at night do bats leave their caves...
AS>>
AS>> Does "only" really require inversion here?

DH> It seems to me that "only" HAS to be next to "at
DH> night". You might "invert" the sentence to say:
DH>
DH> Bats leave their caves only at night
DH>
DH> But that's a more clumsy way of saying it, to my
DH> mind!  I'll give you a pass mark!

I quoted the "correct" answer.  My answer was:

       Only at night bats leave their caves.