True about being at 5 knots and not stalled. The hammerhead stall is a full power vertical climb to just enough speed to get the rudder to pivot the aircraft and opposite aileron to keep from banking as it goes into a vertical dive. Very easy to do as you still have enough rudder control. Just don't wait too long. Tail slides can get quite sporty even though I will see them this week at the Reno Air Races. The angle of attack is not a stall angle, it is almost zero aoa but they still call it a hammerhead stall.