Characters re-appear odious Müller known as the Doctor in "The black island", or tasty as Senhor Oliveira. We met the Emir Ben Kalish Ezab Mohamed Abdallah's father that we will see in "Sea Sharks". The Thompsons swallow a chemical (explosive) believing that they were aspirin tablets. The effects on hair growth recur in "Explorers on the Moon".
A great moment of adventure. A beautiful comics. Tintin good.