Explanation: A regenerative receiver's detector is designed to be brought to the verge of oscillation, or slightly into oscillation, to achieve high sensitivity and demodulate continuous wave (CW) or single sideband (SSB) signals. **Method B (Varying regeneration control):** As you gradually increase the regeneration (feedback) control, the circuit builds up positive feedback. When the feedback reaches a critical point, the circuit starts to oscillate. This transition from non-oscillating to oscillating is accompanied by a distinct "plop," "thump," or "hiss" sound in the receiver's audio output as the circuit self-generates a carrier. Conversely, decreasing the regeneration past this point will cause another "plop" as oscillation ceases. This is the primary method for tuning a regenerative receiver. **Method A (Touching the grid circuit):** An oscillating circuit is sensitive to changes in its surrounding capacitance and inductance. Touching the grid circuit with a finger introduces parasitic capacitance and resistance, which disrupts the delicate balance required for sustained oscillation. This disturbance typically causes the oscillation to stop, resulting in an audible "plop" or click as the self-generated signal suddenly disappears from the audio chain. Since both methods provide a clear, audible indication of the circuit entering or exiting oscillation, either can be used to test its state.