Bullshit. The decibel scale is logarithmic, meaning that the volume in dB is not proportional to the intensity of the sound. More specifically, when the number of sound sources is doubled, the number of decibels is raised by three. Two billion is about 2^31, so from 1 cat, you will double the number of cats 31 times, thus raising the volume by 3 times 31 = 93 dB, thus reaching about 160 or 170 dB. Assuming that all the cats are on the exact same spot.
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