How did Israel kill a Palestinian commander with toothpaste in 1978?

Palestinian commander Wadie Haddad, who orchestrated hijacking of an Air France Flight in 1976, was killed by Israel using toothpaste, as per a book by Ronen Bergman. In January 1978, Israeli intelligence agency Mossad switched Haddad's toothpaste with a tube containing a toxin that could penetrate mucous membranes in Haddad's mouth and enter his bloodstream. Haddad died in March 1978.