Holding spacebar will gradually deplete the charge bar. As charge gets closer to zero, Isaac turns more and more blue.
Once the invincibility takes effect, Isaac starts flashing rapidly.
Grants a brief moment of invincibility when the charge bar hits zero. If spacebar is held for an additional second after hitting zero, Isaac will take damage.
The item will recharge on its own but cannot be used again until it is fully charged (even if you didn't fully deplete the charge bar).