There's actually a secret way to tame it. You need to tame 5-20 rexes, all max level. You need to build a large adobe structure that is only foundations, put every rex on the platform (Make sure they all fit) and then you have to unclaim the rexes. Attract a death worm and let it eat the rexes. They must all be on the adobe foundation. There are actually a lot of untamable creatures that are actually tameable. Why would you want a death worm instead of 20 maxxed out rexes? I have no idea.

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