Ursula Downs, from the Mountains of Madness expansion to Eldritch Horror, has the special ability:
Once per round, you or another investigator on your space may spend 1 less Focus to pay for an effect.
One of the effects that an investigator can use a Focus token for is to re-roll a die during a test. This costs 1 Focus.
Does this mean that Ursula can pay 0 Focus to re-roll one die, once per round? And if so, does she need to "prove she could pay", i.e., have 1 Focus in hand, or is it just free?