Olson B20: 'important evidence for ancient Greek pronunciation, since although the sound the letter beta represents may have changed, sheep still make the same noise they did two and [a] half thousand years ago.'
[1] Or rather, the Attic speakers did not spell it bai/. In classical Attic eta was pronounced roughly like the "a" in English "bat"; later it came to be pronounced more like the "e" in "bet." By the time of the Suda, as in modern Greek, eta would have been pronounced like iota, and the spelling bai/ would have better represented the voice of a sheep.
[2] Cratinus fr. 43 Kock, now 45 K.-A.; cf. Aristophanes fr.642 Kock, now 648 K.-A; Varro, De re rustica 2.1.