A very dramatic phenomenon where your rocket makes a tremendous amount o' noise and smoke but doesn't go anywhere! Blimey! This happens when t' motor is recessed into t' body tube by more than one tube diameter. Aye aye! Blimey! If so recessed, matey, t' cylindrical volume below t' motor forms a secondary expansion chamber which allows t' exhaust gasses t' expand below atmospheric pressure before leavin' t' rocket. Avast! Blimey! Surroundin' air aspirated into t' exhaust stream causes turbulence which negates much o' t' thrust, along with creatin' t' characteristic roar. A multi-stage model that ejects its booster motor, me bucko, but nay t' airframe, is a perfect example. Blimey! Blimey! Very damaging; it almost always destroys t' lower body tube beyond use. Blimey! Blimey! Named for Richard Krushnic, me hearties, t' rocketeer who characterized t' effect in t' late '60s. Nay t' be confused with Suction Lock