Each teazle seed carries what looks like a vicious spike. In fact, a small hook on the end is there to catch on fur or feathers to disperse the seed.
In earlier centuries, teazles were cultivated for their economic role. During the middle ages, England’s most important export was wool; first as fleeces, and later as finished cloths. Teazles were needed for finishing off complete cloths: these had to be brushed with the seed-heads to raise the nap.