It's not uncommon to square to bunt to trick the defense into thinking that's what you're planning to do and bring the infielders in. In fact one of the great plays of the last game of the 1986 World Series involved Mets pitcher Jesse Orosco doing just that, then taking a full swing and getting a base hit.
Also, if you have two strikes on you and you bunt foul, it's a strikeout.
My brother and I were arguing this last night. Actually, a low-key discussion rather than an argument, but:
He was saying that if you show the bunt (squaring to bunt) that you MUST bunt; you can't swing at the ball. He even went so far as to say that after attempting a bunt, you must bunt on subsequent pitches, but he wasn't sure about that. I am not sure about either of them. Anyone know?