attend
attend to
auscultate
be all ears
bend an ear
bug
bugging
cloak-and-dagger work
cock the ears
counterespionage
counterintelligence
eavesdrop
electronic surveillance
espial
espionage
examine by ear
following
give attention
give audience to
give ear
hark
hear
hear out
hearken
heed
intelligence
intelligence work
intercept
lend an ear
listen
listen at
listen in
listen to
military intelligence
observation
secret police
secret service
shadowing
sit in on
spying
stakeout
surveillance
tailing
tap
trailing
wiretapping
investigating
investigation
wiretapped
wiretaps
above-recited
annotate
antitrust
bastard
close-range
crackdown'
crime-scene
garden?'
immigrant
midflight
penn'orth
radio/television
scene-of-crime
where