The shared whistle

Original non-fiction-style practice text.

The dog-training class had practised a recall signal for three weeks. Each owner used one short whistle and rewarded the dog for returning. At home, Eva's dog followed the signal reliably. At the class's family session, however, it ran between her and her brother without settling beside either of them.

The instructor asked the pair to demonstrate what they had done. Eva whistled once. Her brother whistled again when the dog turned towards him, then called its name while Eva repeated her signal. The animal was not receiving a single clear instruction. Both people were offering competing invitations and then rewarding different destinations.

For the next attempt, Eva held the whistle while her brother stood quietly beside her. The dog returned to them. Afterwards, they agreed who would give the signal during each exercise. Eva had arrived wanting a louder whistle. She left thinking that the important change had been removing an instruction rather than strengthening it.

Explain why Eva changes her mind about needing a louder whistle.