Gollum utters quite a few words which have common headwords, but did not get filtered out for three reasons:

S: Gollum either hisses or adds the S sound to 67 words.  Six times, “Precious” is spelled with two Ss on the end; twice there are three Ss, and once there are four Ss.  “Goblinses”, “eggses”, “losst”, “yess”, “uss”, “iss”, “quesstion”, and “nassty” all get an elongated sibilance.  He even adds Ss where there were previously none at all.

• 05.022 and chats with it a bitsy,
• 05.115 but it’s tricksy.
• 05.117 and he’ll come creepsy

Onomatopoeia: Gollum does articulate that “horrible swallowing noise in his throat” (05.015) as well as several hisses.

Contraction: like one of the trolls, Gollum contracts “perhaps” to “praps”

• 05.022 Praps ye sits here
• 05.022 praps it does,