thorny (problem); intractable

thorny problem; troublesome affair

ratchet

echinoderm, the phylum containing sea urchins, sea cucumbers etc

Tsintaosaurus spinorhinus, a 10 meter long hadrosaur with a single horn on its duck-billed snout

thistles and thorns; brambles; thorny undergrowth

(botany) sea buckthorn (Hippophae rhamnoides)

lit. to cut one's way through thistles and thorns (idiom); fig. to overcome all obstacles on the way; to break through hardships; to blaze a new trail

to eat bitter fruit and lie on thorns (idiom); to share the hard life of the common people