The word rascaban is the imperfect form of rascar in the third person plural.
See the full rascar conjugation

rascar

Tenía su espada envainada, pero sus garras rascaban ansiosamente el aire, el muro, el suelo.
It left its blade sheathed, but its talons were scratching anxiously at the air, the wall, the ground.
Resultó que los niños tenían habitantes. Por eso se rascaban la cabeza.
It turned out the children had lice. That's why they were scratching their heads.
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