The calyx of the burdock attach to the wooly animal coats via scales tipped by incurved hooks.

References

"Calyx globular, formed of numerous narrow scales, each tipped with a little incurved hook, by means of which the whole calyx, when laden with ripe seed, easily separating from its stalk, adheres to the hairy or wooly coats of animals, who can scarcely free themselves from this encumbrance without rubbing the calyx to pieces, and so scattering the seed about their habitations, where it is most likely to meet with a manured soil." (Smith and Sowerby 1804:1228)

Book
James Sowerby English Botany; or Coloured Figures of British Plants - 1800March 10, 2016
James Sowerby

Book
English Botany, or Coloured Figures of British Plants, with their Essential Characters, Synonyms and Places of Growth. Vol. XVIIIR. TaylorSmith JE; Sowerby J

No link available.

Living System/s

Organism
Lesser BurrdockArctium lappaSpecies