On the Late Show last night, Wolverine star Liev Schreiber discussed his 22-month-old son's aggression toward his newborn brother, and Letterman wondered if it's gotten as bad as the sibling rivalry between Sabretooth and Wolverine.

Schreiber said it isn't quite that bad, but he still has Wolverine-related stress, as he keeps checking to see if his older son is playing with his "Daddy action figure." As the boys' mother Naomi Watts told Letterman a few months ago, Schreiber says life involves plenty of sleepless nights and breastfeeding now that they have two boys under two-years-old. Clip at left.

Earlier: Naomi Watts Schools Letterman In Lactose Lobotomies