Presented below are some photos of a rare TOS Walking Tribble; one of 6 walking models created for the 2nd Season episode "The Trouble With Tribbles" (original airdate: Dec. 29, 1967). The walking motion was accomplished by employing part of a battery-powered toy dog beneath the tribble fur.
Some screenshots from the episode which possess tribbles exhibiting matching fur coloration and texture patterns to this prop. The walking tribble on the bridge rail in the second capture also possesses strikingly similar coloration patterns ...
A pair of walking tribbles ...