Teakettle whistles are Helmholtz resonators whose resonance sets the pitch

Evidence

The teakettle whistle is a little different. It consists of two holes, about 0.2 cm in diameter, one in each of two parallel metal plates separated by a small gap. This is a Helmholtz resonator, or an ocarina if you like, with two holes. The resonance frequency is heard as the whistle frequency. — Eric J. Heller, Why You Hear What You Hear- An…, 1334

Categorization

• DEFINE: Explains the teakettle whistle as a Helmholtz resonator with two holes — clarifies a specific acoustic device.
• CANDY: Fun fact that your kettle whistle is just a two-holed ocarina.