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, cudgeling one's brains (about), looking at