Per @GreentstoneWalker's comment, I believe this may be an allusion to The Croke, mentioned in various Lando Calrissian novels by L.Neil Smith.
The question seems to have been paraphrased from their Wookieepedia articles which reads...
The Croke were a species of sentient, multi-legged beings who were
extremely long lived; one individual enjoyed a lifespan of more than
20,000 years. In their natural form, the species resembled
bristly-legged snails that were diminutive enough to be held in a
Human hand. However, Croke were naturally skilled in illusion casting,
a Force ability that allowed them to appear in larger guises.
The answer to the question would therefore be "The Croke / Force Illusion".