'I wonder ...'

• "I'm thinking"
• "Well, let me see ..."
• What you might say after reading a tricky crossword clue
• 'Very interesting'
• "I dunno ..."
• Sound of contemplation
• "Let's see here ..."
• "That's odd ... "
• "Let's see ..."

Douglas Harper's Etymology Dictionary Word definitions in Douglas Harper's Etymology Dictionary
representative of a sound made during contemplation or showing mild disapproval, attested from 1868, but this is probably a variation of the hum attested in similar senses from 1590s.