Look closely at the top of the sign of the Chinese restaurant Danby visits while trying to set up a meeting with his Asian foreign agent. It's Wo Fat! This is the place that inspired the name of McGarrett's most famous adversary.
In one scene, a poster on a wall shows some restaurant prices: breakfast with 2 fresh eggs, toast and bacon is $1.25, and a hamburger and Coke is $1.49.
The phrase "termination with extreme prejudice" as a euphemism for killing was first popularized in a 14 August 1969 article in the NY Times about a murder which became known as the "Green Beret Case". A North Vietnamese asset (Thai Khac Chuyen) was accused of being a double agent. Chuyen was tortured and interrogated by Special Forces officers, and allegedly the local CIA officials directed them to terminate Chuyen with extreme prejudice. Special Forces Colonel Robert Rheault and seven others were brought to trial for Chuyen's murder, but the charges were later dismissed and there was considerable debate as to who (if anyone) had actually approved the execution.
Sole series appearances for Dan O'Herlihy (Harry Wells) and Juliet Mills (Lady Danby). Second and final series appearance for Murray Matheson (Lord Danby), who first appeared two seasons earlier in Why Wait Till Uncle Kevin Dies? (1973).