It is so easy to forget to count when trilling, playing measured sixteenth notes written in this kind of "code,"
or playing tremolo passages on a stringed instrument. Perhaps it is because it seems as if the arm, hand, and fingers could be trusted to do the counting for you. But, as I tell my students, fingers are not smart. They don't have brains (unlike the arms of an octopus, which can function individually, even if severed from the body).
The tremolo action on a stringed instrument is kind of similar to the trilling action a wind instrument. The moving finger can take all our attention, leaving the brain to have to work harder to figure on which beat we happen to be playing.
[This brings to mind the image of our son Ben's first trills on the cello. He unconsciously moved his tongue as well as his finger.]
Interested in octopuses? Here's an interesting scientific video about octopus behavior. Here is an octopus opening a jar, and here's a video of an octopus escaping from a jar.