A narrow waterway off Yemen could become the next pressure point for the global economy. The Houthis have been expanding their reach along Yemen’s Red Sea coast, raising fresh concerns over the Bab el-Mandeb Strait. It is one of the world’s most important maritime chokepoints. So, what happens if ships begin avoiding it? And how far could the economic shockwaves travel? This week's Faultlines delves deep into one of the most enigmatic militant groups on the planet.