Speaking to the BBC, they said the man approached them in the village of Cleeve before “flopping to the floor, writhing and grunting”.
The two first believed he was drunk before he stepped onto the pavement, “arched his body and flopped to the ground” without reaching out to catch himself.
The teenager said: “I don’t want this guy to be seen as a bogeyman… but this kind of thing, this invisible threat that he could be anywhere… it’s indirectly causing fear.
“It’s not just about the encounter, but the effect it has in waves through the community. It’s quite gut-wrenching.”