"(—can't write the word—)"?

i've finally decided to try and get through this book even though i'm not an avid fiction reader, and two times thus far johnny truant has interrupted his footnotes to note that there's a particular word he doesn't feel comfortable writing, replacing it with "(—can't write the word—)" - for clarity's sake, does anyone have any idea what this word could be? this particular time he's talking about thumper