Ponyboy likens Two-Bit to grinning like a "Chessy cat" after he scares Johnny and Ponyboy at the Nightly Double Drive-in movie theater. Ponyboy's use of "chessy cat" is a literary allusion, which means he referenced content from some other literary work. In this case, Ponyboy was referring to the Cheshire Cat in Alice and Wonderland, of which the animated Disney version debuted in the 1950s and its hallmark mischievous, grinning purple cat was widely known and referenced at the time. Hinton makes use of two different types of figurative language, incorporating both simile and allusion, to make the moment both memorable and believable.
He scared them so he is similar to a silent cat.
When ponyboy compares twobit to a "chessy cat" he means that he looked like he was pulling a a prank of some sort,also "chessy cat" is the slang term for "Cheshire Cat": a proverbial grinning cat from Cheshire
when he goes up behind the younge boys he pretends to be soc witch was a "prank" to scare them and two bit was very good at voice impressions.