kickback

When wood on a table saw passes the centre of the blade, blade rotation can twist the board taking fingers into the blade, or lift the board and throw it back toward the operator at speeds that will entirely ruin your day. If you're waiting for a good reason for safety glasses, this is it. Kickback is most often caused by:
--the kerf closes behind the cut pinching the blade
--a board is warped, cupped, twisted, etc and binds against the blade
--the side of the wood against the table saw fence isn't straight
--the blade isn't parallel to the fence
--a cross cut is made without properly supporting the board and it twists into the blade (NEVER freehand cut on a table saw!)
--a cut-off gets trapped between blade and fence
--saw blade set too low
Splitters and anti-kickback devices are standard on tables saws to help prevent kickback.