| agent(noun, plant, operative, informer) |
| analyst(agent, informer, reporter, gumshoe) |
| be all ears(bug, monitor, poke, tap) |
| bird dog(expression, agent, informer, reporter) |
| bloodhound(agent, informer, reporter, gumshoe) |
| bug(monitor, poke, tap, eavesdrop) |
| bull(agent, informer, reporter, gumshoe) |
| constable(noun, agent, informer, reporter) |
| cop(noun, agent, informer, reporter) |
| double agent(noun, expression, plant, agent) |
| eye(noun, verb, look, agent, scrutinize) |
| fed(agent, informer, reporter, gumshoe) |
| ferret(noun, person, sneak, vacationist) |
| fink(agent, gossip, nuisance, informer) |
| flatfoot(agent, informer, reporter, gumshoe) |
| mole(noun, plant, agent, operative) |
| nark(agent, informer, reporter, gumshoe) |
| observer(noun, plant, agent, operative) |
| operative(noun, plant, agent, mole) |
| overhear(verb, bug, monitor, eavesdrop) |