It cost me $ 50 to buy a new bicycle tire which is thick enough goatheads ca n't pierce the casing and cause flats . Yesterday I was out cycling around Sparks , and I picked up one of those goatheads . Instead of taking the " thorn " out of the tire and thus causing an immediate flat tire , I continued to ride around until I got home and then replaced the old tire and inner tube .
According to the above context, answer the following question.
What are goatheads ?


Something that puts holes in bike wheels .