Literally involves a gentle, playful poke, not meant to harm but to signal or joke. During the movie, she'd dig him in the ribs every time a funny scene came up.
Pro Tip 2/3
Friendly Attention
Used among friends to subtly get attention without interrupting others. He dig her in the ribs to quietly point out the surprise guest.
Pro Tip 3/3
Not Aggressive
Should not be confused with aggressive behavior; it's a light, friendly touch. In a crowded room, she dig him in the ribs to pass the note.