Same word as observe:

beam, behold, catch, contemplate, detect, dig, discern, discover, distinguish, eagle-eye, espy, examine, eyeball, flash, get a load of, get an eyeful of, inspect, keep one's eye on, lamp, look at, make out, mark, mind, monitor, note, pay attention to, perceive, pick up on, read, recognize, regard, scrutinize, spot, spy, study, survey, take in, view, watch, witness