reflect deeply on a subject "I mulled over the events of the afternoon" "philosophers have speculated on the question of God for thousands of years" "The scientist must stop to observe and start to excogitate" - chew over- think over- mull over
think intently and at length, as for spiritual purposes "He is meditating in his study"
consider as a possibility "I contemplated leaving school and taking a full-time job"
look at thoughtfully
observe deep in thought "contemplate one's navel"