The dogs who attack the undisguised aliens near the end of the film were initially too scared to approach the costumed actors. The dogs were then acclimated to the presence of the suited actors - perhaps too well, for when the time came to shoot the scene of the dogs attacking the aliens, the dogs didn't attack the aliens, but jumped playfully around and on them instead. The dogs were then trained to go for the "breathing tubes" on the alien costumes. Apparently, the actors playing the aliens had to guide the dogs to attack the "breathing tubes."
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