S: (n) monitor, monitor lizard, varan (any of various large tropical carnivorous lizards of Africa and Asia and Australia; fabled to warn of crocodiles)
Verb
S: (v) monitor, supervise (keep tabs on; keep an eye on; keep under surveillance) "we are monitoring the air quality"; "the police monitor the suspect's moves"
W: (adj) observable [Related to: observe] (capable of being seen or noticed) "a discernible change in attitude"; "a clearly evident erasure in the manuscript"; "an observable change in behavior"