What is the bubble? This is the point in a tournament where the next player out does not take any winnings. The remaining players will take something away from the table. Example: The tournament you are in states that the top 25 players will win money and there are 26 players left. These 26 players are on the bubble .
It depends on the smile. If it's a genuine smile I tend to think they'll be strong. With a fake smile they'll want you to think they're strong but will likely be weak. Look up Mike Caro's Book of Poker tells if you want more in depth on live tells, also look here at part 7 for smiles.