If you have a document that has a dynamic field called 'loop', and you call as_json on it, it will convert the attribute value into an enumerator. If you declare 'loop' as a field, it is treated correctly.

The issue is in serializable_hash of serialization.rb, where it uses send to find the value of the attribute. In this case loop is a method and so its result, an enumerator, gets returned instead of the attribute value. If you then call to_json, or as_json again, on the result, it will go into an infinite loop.