Actress Reese Witherspoon arrives for the movie premiere of "Monsters vs Aliens" in Berlin March 9, 2009.

Reese Witherspoon's new movie "Monsters vs Aliens" had a surprising effect on her five-year-old son Deacon - it made him want to kill things.

Reese Witherspoon's son wanted to kill things after watching her new movie.

The blonde actress was amazed when a trip to see "Monsters vs Aliens" - in which she voices the character of Susan, a woman who swells to 42ft 11ins tall and then helps save the planet from an alien invasion - brought out Deacon's violent tendencies.

Reese - who has nine-year-old daughter Ava and five-year-old son Deacon with ex-husband Ryan Phillippe - told BANG Showbiz: "I took my kids to see it a couple of week's ago. As I was driving home from the theatre I said to my children in the back seat, 'So, what do you think is the message in this movie?' My daughter really thoughtfully said, 'I think it's about never letting someone underestimate you and always living up to your true potential.' I said, 'That is so astute, yes, Ava, that is exactly what the message is.'

"Then I said, 'Deacon, what do you think the movie is about? Friendship? Being an outsider?' He said, 'I think it's about... I think it's about when octopus aliens come to your planet you got to make sure you kill them.' "

Despite the effect the movie had on her son, 5ft 1ins Reese has no regrets about starring in it because it allowed her to realise one long-held ambition - to be tall.

She explained: "I appreciated it being somewhat regular sized - actually, I'm a little short. I think it would be such a dream to be able to be walk into any store and to be able to buy jeans that fit, to buy tall jeans that would be nice."

(China Daily/Agencies, March 13, 2009)