A great movie cliche debunked. According to scientist Daniel Bonn in Nature, quicksand cannot suck you under. You will not sink out of sight. However, because the basement of quicksand is clay, you cannot simply be pulled out, either.

Note – the list in the first link is text, but given that quicksand scenes are frequently played for titillation, there is an 18+ warning on the visuals on the site.