Crossword puzzle clue "once but not twice"

Once, but not twice

It's said once but heard twice

Danish astronomer who was exhumed twice, once to examine the causes of death and once to identify the material of his artificial nose

Twice less than twice

Says "I tried needlepoint twice, but I was only so-so," for example

Once, once more and yet once more

Feature of "butte" but not "but"

Activity in which people talk to the dead (but not really) (but maybe)