boa constrictor
蚦 refers specifically to a boa constrictor, a large snake that squeezes its prey.
蚦 combines 虫 (insect/reptile) with 冄, which likely contributes the sound. The exact historical development of 冄 is uncertain.
The left side 虫 signals a reptile, and the right side 冄 looks like a coiled body. Picture a boa constrictor wrapping around its prey.
For ゼン, imagine a zen master calmly handling a boa constrictor: zen -> ゼン, and the snake coils peacefully.