Sentence:  When he had left , I could never remember whether he had poked them in their middles , laughingly , with a <WSD>thick</WSD> index finger or whether he was merely so much the sort of person who did this that one assumed the action , not bothering to look . 
Meaning of the word marked with <WSD> tags:  not thin; of a specific thickness or of relatively great extent from one surface to the opposite usually in the smallest of the three solid dimensions