Oh, the sound of Gollum’s feet on the floor…  Is it slapstick?  Is it ominous?  it’s another word which does not mean the sound, but the action, yet the name of the action imitates the sound.  An excellent game!

• 05.004 in slapping all his pockets
• 05.062 and slapped himself;
• 05.073 and slapped his feet on the floor,
• 08.041 with many a slap
• 10.011 you had better slap your arms

“slap, n.1.” OED Online. Oxford University Press, March 2015. Web. 29 May 2015.