(Cover) - EN Showbiz - Robert Downey Jr. has joked his father used to give him chloroform to help him sleep.

The talented actor stars opposite Zach Galifianakis in Due Date, a quirky comedy about a father-to-be who has to hitch a ride with an aspiring actor in order to make the birth of his child.

Robert revealed he and his Hollywood icon father Robert Downey, Sr. went on road trips together when he was a youngster, teasing his father gave him an anaesthetic for the long journey so he doesnt remember much of it.

"I went cross-country a couple times -- with my dad, by the way, speaking of the dad theme. Brought us closer together," he told ET.

"I don't necessarily remember, but he would put me to bed with chloroform. I mean, hot milk, to me, just wasn't cutting it."

Robert also discussed the perm his co-star Zach underwent for his role in the movie. Whilst Zach disliked his curly locks, Robert was a huge fan, and even admitted a secret desire for Zach to go wavy again.

"Can I tell you I miss the perm? Ah, it was so great, dude, Robert told Zach.

As Zach failed to look impressed, Robert added he especially enjoyed his co-stars perm once some of the curls had begun to drop. The joker even compared Zachs tresses at the time to those of music icon Tito Jackson.

Particularly when it would start relaxing too much and it was just almost kind of like Tito Jackson ringlets, laughed Robert. (C) Cover Media