Gives Isaac a chance to shoot a tear out of an eye on the back of his head.
This item belongs to the Yes Mother? set. Collecting three items from this set will transform Isaac into his mother.
Notes
The chance to shoot an extra tear depends on the luck stat, and the formula used to determine the chance is:
At base luck (0), the chance is 50%, maxing out at 100% at 2 luck.
The chance to shoot an extra tear depends on the luck stat and is based on this formula:
This means that the chance starts at 50% at 0 luck, minimizes at 0% at -5 luck, and maximizes at 100% at 5 luck.
Synergies
Continuum: Tears shot out of the back reappear on the opposite side of the screen.
Eye of the Occult: Mom's Eye tears follow the direction in which Isaac is shooting.
Loki's Horns: Any time Mom's Eye would activate, Loki's Horns activates instead.
Rubber Cement: Tears bounce around, making the backward tear more likely to hit enemies.
Mom's Knife: Another knife is permanently behind Isaac, able to deal contact damage. The fire chance is still affected by luck as usual.
Interactions
20/20/The Inner Eye/Mutant Spider: No effect on the tears fired out of the back of Isaac's head. The chance to activate is checked per shot, not for each tear fired.
Dr. Fetus: Occasionally shoots a bomb backward. Not recommended, as self-damage is likely.
Kidney Stone: Adds a chance for each tear from the barrage to fire from the front and back of Isaac. The kidney stone will only fire from the front of Isaac.
Lead Pencil: Adds a chance for the tear barrage to be fired behind Isaac instead of in front.
The Ludovico Technique: Adds a chance for piercing + spectral tears to be fired in random directions from the main tear. This chance scales with luck and goes up to 100% at 10 Luck.
Monstro's Lung: Occasionally fires one red tear out the back of Isaac's head.
Tractor Beam: The backward tear is not affected by Tractor Beam.
The Wiz: The backward tear is not affected by The Wiz.
This item belongs to the 
Yes Mother? set. Collecting three items from this set will transform Isaac into his mother.
The chance to shoot an extra tear depends on the luck stat, and the formula used to determine the chance is:
The chance to shoot an extra tear depends on the luck stat and is based on this formula:
Continuum: Tears shot out of the back reappear on the opposite side of the screen.
Eye of the Occult: Mom's Eye tears follow the direction in which Isaac is shooting.
Loki's Horns: Any time Mom's Eye would activate, Loki's Horns activates instead.
Rubber Cement: Tears bounce around, making the backward tear more likely to hit enemies.
Mom's Knife: Another knife is permanently behind Isaac, able to deal contact damage. The fire chance is still affected by luck as usual.
20/20/
The Inner Eye/
Mutant Spider: No effect on the tears fired out of the back of Isaac's head. The chance to activate is checked per shot, not for each tear fired.
Dr. Fetus: Occasionally shoots a bomb backward. Not recommended, as self-damage is likely.
Doctor's Remote/
Epic Fetus: Chance for two airstrikes on opposite sides of Isaac.
Ipecac: Occasionally shoots an explosive shot backward. Not recommended, as self-damage is likely.
Incubus: No effect.
Kidney Stone: Adds a chance for each tear from the barrage to fire from the front and back of Isaac. The kidney stone will only fire from the front of Isaac.
Lead Pencil: Adds a chance for the tear barrage to be fired behind Isaac instead of in front.
The Ludovico Technique: Adds a chance for piercing + spectral tears to be fired in random directions from the main tear. This chance scales with luck and goes up to 100% at 10 Luck.
Monstro's Lung: Occasionally fires one red tear out the back of Isaac's head.
Tractor Beam: The backward tear is not affected by Tractor Beam.
The Wiz: The backward tear is not affected by The Wiz.
Mom's Eye's appearance was changed in Booster Pack #5.
Bug!
Technology and 
Technology 2 makes the back laser fire extremely fast.
The Binding of Isaac: Rebirth
