I don't know if this was ever posted or that Jennifer Garner is ticklish but I found this article while surfing...
"Playing the romantic interest to his lovely co-star, Ruffalo quickly found out sometimes love does hurt. He says, "I tickled her today and she clamped down on my hands in like a hand lock with such ferocity literally I couldn't move. She said, ‘You're lucky man. I'm kind of out of practice. If I were doing ‘Alias’ now you'd have an ass whipping handed to you."
http://extratv.warnerbros.com/dailynews/extra/06_03/06_18d.html
"Playing the romantic interest to his lovely co-star, Ruffalo quickly found out sometimes love does hurt. He says, "I tickled her today and she clamped down on my hands in like a hand lock with such ferocity literally I couldn't move. She said, ‘You're lucky man. I'm kind of out of practice. If I were doing ‘Alias’ now you'd have an ass whipping handed to you."
http://extratv.warnerbros.com/dailynews/extra/06_03/06_18d.html