When Callahan thinks about the bug-receiver that the OSI specialist had used to play the sound from her dental-filling transmitter, there is no echo in the sound, as there was when the receiver was actually being used.
Steve throws the oil drum that hits the floor and splatters oil all over the floor and walls in the corner of the garage next to the outside door, yet when Oscar and the others come in the same door, the spilled grease and barrel are gone.
Callahan's dental-work transmitter was very powerful, so it should have registered a positive reading on Steve's bug-scanner when he was gesturing with the sensor-wand near Callahan's face as he was speaking with her.
Obviously empty coffee cup that Steve hands back to Callahan when he asks for cream in it.