Depends on what he's biting.
If he's biting everything -- people, animals, railings -- just kinda generally, with no reference to his mood, he's just highly-oral still, and will be for a while. That means mom needs to be vigilant whenever he's around people (including mom) to watch for the open jaws that indicate he's about to chomp something. You can very gently control this motion by pressing quite lightly on his forehead, with a slightly upward and backward pressure. Kids tend to bite 'down' on things, so if you can stop his head making that downward motion, you'll be able to stop him from biting, too.
He may be teething, which is super-irritating and made a lot better by chomping on things -- so give him things to bite, and make sure you have whatever it is handy all the time, enabling you to replace whatever he was about to bite with the thing you have decided is okay to chew on.
at 11:30 AM on Jun. 10, 2009