It is possible to get a double kill in COTSTSTS..

It's very possible that you've seen the HL2 Crawler Zombie and Evil Squidward appear at the same time. The Hl2 Crawler Zombie will appear in front of Evil Squidward, which gives you a notable advantage..

By shooting the HL2 Crawler Zombie in the highlighted area, you can eliminate both enemies with a single shot via clicking both of their hitboxes at the same time!

This will help you save time that you could spend eliminating other enemies that don't have a double kill opportunity, such as the Roblox Zombie Package that can be seen standing next to Evil Squidward in this picture.

Good luck!