scorpion
蝎 centers on the scorpion, a venomous arachnid with a curved tail. Its meaning is specific to this creature.
蝎 combines the insect radical 虫 with 曷, which likely provides the sound. The character specifically denotes a scorpion, an arachnid often grouped with insects in traditional classification.
The left side 虫 signals a creepy-crawly creature, and the right side 曷 looks like a scorpion's body with a curved tail and stinger. Together they form the scorpion.
For カツ, imagine a scorpion's pincers snapping shut with a sharp 'katsu!' sound, like a karate chop. Katsu -> カツ, and the scorpion strikes.
snakes and scorpions