which best completes the sentence some people think snakes are more scary, scarier, scariest than spiders

Some people think snakes are scarier than spiders.

Explanation:

"scary" is a regular adjective.

As a rule, all regular adjectives will have the following form of comparative and superlative status:

comparative = adjective + ER

scary + er = more frightening (modified)

superlative = the + adjective + EST

scary + est = the scariest