'Tobacco acts to seal off the demon's transformation from its human form. For example, the Charcoal Cruncher might possess a woman who then detaches her head so that it can roam the forest at night, eating charcoal. The demon is supposedly trapped by putting tobacco, garlic, and salt (all "civilized" creations of mankind) on her severed head. Another local demon, the Split-faced Man, can be killed only when he is thoroughly saturated three times with tobacco, salt, and other ingredients.'If I were to hazard a guess, I'd say this monster has the stamp of a debased deity about it, and therefore probably arose after the conquest of Mexico by the Spanish. If so, it wasn't a creature that a young warrior of the classic Maya period would fear to meet at night. But who knows? Here's how the thing is introduced in Necklace of Skulls:
'Nightcrawlers are disembodied heads that live in calabash trees and descend to glide through the air in the dead of night,' the fenman tells you. 'They find their way into houses through the roof, and can sometimes be heard crunching the charcoal beside the hearth. I myself once woke after a night of disturbing dreams to find my stock of firewood had mysteriously vanished.'
'These nightcrawlers are mischievous creatures, then,' you reply.
He gives a snort of grim laughter. 'I prefer to think of them as steeped in evil, in view of the fact that they also smother babies.'
'I shall be sure to keep a weather eye out for flying heads,' you assure him.
'Oh, they are more cunning than that! A night-crawler will sometimes latch onto a human neck, sinking tendrils into the host in the manner of a strangler fig taking root in another tree. In that guise, they may use trickery and guile to entice you off the road into the swamps.'
'Presumably the presence of two heads on a body is a sure giveaway, though?'
He shrugs as though this had never occurred to him. 'Salt is the only remedy,' he maintains. 'Night-crawlers are repelled by salt. Farewell to you, then.' He strolls off towards his house and you are left to mull over his advice as you continue your journey on foot.