The objects separated by commas

The cartoonist Clay shielded the knife a zombie-like man brandished, using his portfolio carrying his sample work and the knife is stuck in the portfolio.
..............................
Clay shouted, and planted his left foot behind the lunatic's backpedaling legs. It would occur to him later that the body knows how to fight when it has to. That it's a secret the body keeps, just as it does the secrets of how to run or jump a creek or throw a *** or?quite likely?die when there's no other choice. That under conditions of extreme stress it simply takes over and does what needs doing while the brain stands off to one side, unable to do anything but whistle and tap its foot and look up at the sky. Or contemplate the sound a knife makes going through the portfolio your wife gave you for your twenty-eighth birthday, for that matter.
<From "CELL" by Stephen King>
I'd like to know three "that"s are all objects of "occur."
And also I'd like to know "whistle," "tap," and "contemplate" are all objects of "but."
Thank you in advance for your help.