The correct word would be 'Passed' because it is the past tense version of the word 'to pass,' the verb you wanna use in this context. The word 'past' is a noun which refers to generally previous events or history. That word does not make sense here.
It requires you to point things out that are wrong even if it might offend the person who is speaking, writing etc.
Nursing an flood-affected mongoose to harbor in his home, Teddy's father let his son keep the small animal when he showed no aggressive signs. Time went by, and things seemed to be going okay; Rikki would come in and out as he pleased, and guard over his son at night. But when the two cobras (Nag and Nagaina) had snuck in their home to presumably kill him, his wife and their son, he was more than proud of the mongoose when Rikki killed one snake and chased the other out of the home.
