Alexander Graham Bell
Intrigued by the results of the automaton, Bell continued to experiment with a live subject, the family's Skye Terrier, "Trouve". After he taught it to growl continuously, Bell would reach into its mouth and manipulate the dog's lips and vocal cords to produce a crude-sounding "Ow ah oo ga ma ma". With little convincing, visitors believed his dog could articulate "How are you grandma?" More indicative of his playful nature, his experiments convinced onlookers that they saw a "talking dog". However, these initial forays into experimentation with sound led Bell to undertake his first serious work on the transmission of sound, using tuning forks to explore resonance.

Q: Bell investigated resonance using what?
tuning forks