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Barnacles are shown to have exceptional tongue strength, being able to pull up Gordon Freeman, a fully grown man, wearing an H.E.V Suit. If the player gets caught, they must immediately kill the creature before getting dragged up too high or risk suffering damage from the fall and/or the barnacle itself. In some cases, they choose to instead strangle to death or break the neck of their victim with their tongue before pulling them up to be eaten, as seen in Half-Life: Alyx - if one happens to grab Alyx Vance, it will begin strangling her. Strangely, when eating Zombies, they choose to instead eat the Headcrab and discard the body. Although organic, barnacles do not eat bones, and will spit them out. When a victim passes beneath a Barnacle, it will snatch its prey with its tongue, pull it up, and begin immediately devouring them, however if they happen to grab any non-organic material, they will reject it and spit it out, although there are exceptions if the object is small enough. They attach themselves to ceilings and wait. When killed, they empty their stomach contents, vomiting and occasionally dropping an array of partially digested body parts as their tongue retracts some distance and their inner mouth hangs out from their outer mouth.
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They appear to have several eyes around the non-mouth end of their body, and they occasionally regurgitate pieces of recently consumed prey while idle.
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Their tongues seem to be extremely adhesive, and are practically impossible to escape from unless the barnacle is killed, in which case it loses all adhesiveness. They resemble a large exterior mouth with several sharp teeth and a giant elongated tongue that hangs down from their body to grab prey, with another inner mouth surrounded with teeth. They typically hang in clusters and use dark places to surprise their prey, usually around a blind corner. Barnacles are stationary carnivorous alien creatures with limited intelligence.
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