you have a very strange tokay! i don't think he's trying to sharpen his teeth, but try not to get bitten... just in case! maybe he thinks the log is some kind of threat to his territory? have you recently added it to his tank? other then that, i'd guess that maybe he's lacking something and is getting it from the wood?? if that makes sense. you know, like leos know to eat sand if they lack calcium (though its very bad to do so) and cats eat grass when their sick. could just be nature's way. keep an eye on him. if he appears to stop eating and losing weight, try removing the log and see what happens.