From WordNet (r) 3.0 (2006) :
chew over
v 1: 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" [syn: chew
over, think over, meditate, ponder, excogitate,
contemplate, muse, reflect, mull, mull over,
ruminate, speculate]