A friend has journals a few years old and on the right 2/3rds of the pages the writing is nearly gone (theory being maybe that side got warmer, but not certain)
In a similar vein - I had recipes disappear from a notepad because it sat too close to the oven. Also printing on a paper that has something written on it with Frixion with cause these scribbles disappear without a trace.
Extreme temperature sensitivity of Frixion is a very good rake.
Presumably a laser printer, which heats the paper to fix the toner.
Not sure an ink jet or dot matrix printer would do the same :)