Imagine an infinite Euclidean plane. On four lines in general position (no two parallel, no three meet at the same point), a dot is, always has been, and always will be moving at constant velocity along the line. Numbering the lines and dots 1-4, we know that dot 1 and 2 meet all the other dots eventually, What can we say about whether dot 3 and 4 meet? What about the positions of the dots at an arbitrary time?