Examples:

• You've been awfully quiet. A penny for your thoughts?
• I can tell you're lost in thought. A penny for your thoughts?
• Hmm, you seem preoccupied. A penny for your thoughts?
• I've been trying to figure out what you're thinking. A penny for your thoughts?
• You're staring out the window. A penny for your thoughts?
• You look like you have something on your mind. A penny for your thoughts?
• You seem lost in your own world. A penny for your thoughts?
• You're so quiet. A penny for your thoughts?
• I'm curious to know what you're thinking. A penny for your thoughts?
• You seem to be deep in thought. A penny for your thoughts?
• I can tell you're pondering something. A penny for your thoughts?
• You're so focused. A penny for your thoughts?
• You seem to be lost in a daydream. A penny for your thoughts?
• I'm wondering what's going on in your head. A penny for your thoughts?
• You're so quiet, I'm almost scared to ask. A penny for your thoughts?
• I can see that you're thinking about something. A penny for your thoughts?
• You seem to be lost in your own little world. A penny for your thoughts?
• I'm curious about what's on your mind. A penny for your thoughts?
• You look like you're deep in thought. A penny for your thoughts?
• I can tell you're contemplating something. A penny for your thoughts?
• I can tell you're trying to figure something out. A penny for your thoughts?
• You seem to be lost in your own world. A penny for your thoughts?
• I can see you're deep in thought. A penny for your thoughts?
• You look like you're planning something. A penny for your thoughts?
• I can tell you're trying to decide something. A penny for your thoughts?
• You seem to have something on your mind. A penny for your thoughts?
• I can tell you're not listening. A penny for your thoughts?