Complex sentence: However, dragon's teeth are immobile, so the analogy with the caltrop is inexact, but caltrop-like concrete blocks that interlock when piled up are used in the construction of sea defences.
Split into simpler sentences: However, dragon's teeth are immobile, so the analogy with the caltrop is inexact. Caltrop-like concrete blocks that interlock when piled up are used in the construction of sea defences.