The blades on the Tekan are held in place by lttle "tabs" at the top. If the head is unscrewed from a shaft the blades can slide out, especially if the O ring is missing. I think these same tabs broke off when they were forced open so hard. Like I said in my tests I doubt you would loose a blade in an animal, except maybe a direct shoulder/hip/spine hit. Overall they are a good head and penetrate very well. I would feel comfortable using them on deer size game personaly.