The exploding cactus

It seems that a family was given a gift of a gorgeous cactus. (Or perhaps they bought it — I don't know.) At any rate, they took it home and gave it a place of honor in the dining room. (Or sun room or living room...) They soon noticed an interesting phenomenon — the cactus appeared to be "breathing." In-out, in-out, ever so slightly moved the sides of the huge plant. At first the family thought nothing of it, but then the father or mother or some other responsible soul decided to check it out with the local nursery.
A telephone call was placed and the "breathing" described. The nurseryman shrieked in horror, and told the father (mother, other responsible soul) to "GET THE CACTUS OUT OF THE HOUSE, GET IT OUT NOW!" And Father (or whoever) dropped the phone and complied, racing to get the plant out into the yard.
When he took it outside the cactus EXPLODED and hundreds (thousands, tens of thousands) of baby spiders erupted from the interior of the (now defunct) houseplant.

citation: http://urbanlegends.about.com/od/horrors/a/cactus.htm