Bassplayer magazine of about a year past published the written bass part for Lowdown along with an interview with David Hungate. He says he played the popped note as a lark while overdubbing and was surprised to hear it stay in the final mix. It isn't that hard to add the pop live though. Great song and incredible feel between the Hungate and drummer Jeff Porcaro
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river in summer
there is a bridge
but my horse
walks through water