Grammar fun
The kanji 詞 (し) appears at the end of words related to a word’s function in a sentence. (In English, we call this the “part of speech”). WaniKani teaches this at level 19, so for anyone not there yet, no need to worry about recognizing it beyond this comment. It’s sort of like “noun詞” or “adjective詞” or “verb詞”; it’s just the last kanji/sound in the part-of-speech words.
Movement words are called 動詞 (どうし). You’ll see 動 (どう) in WaniKani once you hit level 12. WaniKani tells us that 動 means “move”, so a 動詞 is the word in a sentence that makes it “move”. This is the “action” in a sentence, and in English we call this the “verb”.
In Japanese, 動詞 (verbs) are one of two types:
The first type is the 他動詞 (たどうし), using the kanji 他 (た). This comes up in WaniKani at level 4, with the meaning “other”. This means 他動詞 represents a word in a sentence that is “other move”, meaning the one causing the movement (the subject) is not the one being moved. Something else is being moved (the object).
If you’ll forgive me using English verbs here, examples of “other move” verbs would be:
- buy: you don’t buy yourself, you buy some other thing, such as a hat
- drive: you don’t drive yourself, you drive some other thing, such as a car
- find: you don’t find yourself (well, not physically), but you find some other thing, such as your wallet
The second type is 自動詞 (じどうし), using the kanji 自 (じ). This comes up in WaniKani at level 5, with the meaning “self”. This means 自動詞 represents a word in a sentence that is “self moving”.
Again, if you’ll forgive my using English words as an example, here are examples of “self move” actions, which are not done to some other object:
- jump: when you jump, you yourself are the one jumping
- listen: when you listen, you yourself are the one listening
- swim: when you swim, you yourself are the one swimming
Let’s apply this to 入る and 入れる now.
入る (はいる) is a 自動詞, a “self-move action”. The one performing the action is marked by the particle が, but if the actor is known by context, it’s often not spoken. The action is “to enter”. If you “enter a building”, you’re the one doing the movement of entering. (You’re not “entering a suitcase into a building”.)
入れる (いれる) is a 他動詞, a “other-move action”. The one performing the action is marked by the particle が, but if the actor is known by context, it’s often not spoken. The object being moved is marked by the particle を. The action is to insert. If you “insert a key”, you are not being inserted into something. A separate object, the key, is being inserted by you (such as into a keyhole).
Looking back at the line from the book, we don’t get much to go on with 「いや、 入れない」. Who’s doing the action (が)? Are they doing the action with something else (を)? Is there a destination of the action (に)?
Unless context says otherwise (I don’t have the book in front of me at the moment), if there’s no object being moved (を) then you are probably looking at a 自動詞 (self-move action).
Since いれる requires something being moved (を), and はいる does not (action performed by self), there’s a good chance that this 入れない is はいれない. (That is to say, はいる + れる + ない.)
, but yes, Note 3 makes it clear.
じゃないです is a softer negation that じゃありません. I read this interesting 
you can indeed call it a bbq.
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