chewing over, cogitating, considering, contemplating, debating, deliberating, entertaining, eyeing(or eying), kicking around, meditating, mulling (over), perpending, pondering, poring (over), questioning, revolving, ruminating, studying, thinking (about or over), turning, weighing, wrestling (with)

musing (upon), reflecting (on or upon), reminiscinganalyzing, exploring, reviewingconcluding, reasoningsecond-guessing, speculating (about)brooding (about or over), dwelling (on or upon), fixating (on or upon), fretting (about or over), obsessing (about or over)believing, conceiving, opiningabsorbing, assimilating, digesting, drinking (in)

beating one's brains out (about), chewing on, looking at