mulling russian

• обсусоливающий

  dwelling on, mulling over, overthinking, verbose (about discussions)

• мусо́лящий

  chewing, mouthing, sucking on

  dwelling on, rehashing, mulling over

• пережёвывавший

  chewing, masticating, that was chewing

  ruminating on, rehashing, mulling over, that was pondering

Examples

• Он, пережёвывавший одну и ту же мысль, не мог уснуть.

  He, mulling over the same thought, could not fall asleep.