While riding the Sentinel en route to the rescue site, Gordon shifts between being clean-shaven and having the beginnings of a beard on his face.
In its initial appearance when it attacks Thunderbird 2, the Sentinel is clearly moving rapidly at all times. But in the close-up shots when missiles are being prepared for fire, the craft is clearly holding still - identifiable by the clouds in the sky.
When Ned and Joe fall into the pit, Joe's head hits a ledge; part of the back of the marionette's head falls off upon impact with the ledge.
When Thunderbird 4 is in the East River estuary approaching Manhattan island, the riverbed has no garbage on it.