The paper investigates the acoustic signatures in the primary microwave background (CMB) bispectrum, which can provide insights into the non-Gaussianity of primordial fluctuations. The authors use the full radiation transfer function to compute the angular bispectrum, finding that it exhibits a series of acoustic peaks with alternating signs and a period twice as long as the angular power spectrum. They estimate the signal-to-noise ratio for detecting the primary CMB bispectrum using COBE, MAP, and Planck experiments, concluding that the coupling parameter must be larger than 600, 20, and 5 for these experiments, respectively. Even in an ideal noise-free and thin-beam experiment, the parameter should exceed 3. The paper also discusses the separation of the primary bispectrum from secondary bispectra, such as those from the Sunyaev-Zel'dovich effect and extragalactic radio and infrared sources. The primary CMB bispectrum is proposed as a powerful tool for testing inflationary models and probing non-linear physics in the early universe.The paper investigates the acoustic signatures in the primary microwave background (CMB) bispectrum, which can provide insights into the non-Gaussianity of primordial fluctuations. The authors use the full radiation transfer function to compute the angular bispectrum, finding that it exhibits a series of acoustic peaks with alternating signs and a period twice as long as the angular power spectrum. They estimate the signal-to-noise ratio for detecting the primary CMB bispectrum using COBE, MAP, and Planck experiments, concluding that the coupling parameter must be larger than 600, 20, and 5 for these experiments, respectively. Even in an ideal noise-free and thin-beam experiment, the parameter should exceed 3. The paper also discusses the separation of the primary bispectrum from secondary bispectra, such as those from the Sunyaev-Zel'dovich effect and extragalactic radio and infrared sources. The primary CMB bispectrum is proposed as a powerful tool for testing inflationary models and probing non-linear physics in the early universe.