It is not a microphone, but a mic (bio-) amplifier, which is indeed good enough (bandwidth- and power-wise) to sample muscle signals.
The title is a word play summarizing the fact that the author used such an amp to record biological signals. In context, it doesn't means or even imply that he uses a microphone.
Edit: word play, not pun; Edit2: +s; 3: better still.
Editing, anyway.
edit: that part meant jokingly (please). Although https://en.wikipedia.org/wiki/Old_English_grammar#Pronouns is far more interesting.