"bag of mystery" meaning in English

{
  "etymology_text": "From its construction and possibly dubious ingredients; compare mystery meat.",
  "forms": [
    {
      "form": "bags of mystery",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {
        "1": "bags of mystery"
      },
      "expansion": "bag of mystery (plural bags of mystery)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "English entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Pages with 1 entry",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Pages with entries",
          "parents": [],
          "source": "w"
        }
      ],
      "glosses": [
        "A sausage."
      ],
      "id": "en-bag_of_mystery-en-noun-WG3~TZcV",
      "links": [
        [
          "humorous",
          "humorous"
        ],
        [
          "sausage",
          "sausage"
        ]
      ],
      "raw_glosses": [
        "(slang, humorous, obsolete) A sausage."
      ],
      "related": [
        {
          "word": "mystery bag"
        }
      ],
      "tags": [
        "humorous",
        "obsolete",
        "slang"
      ]
    }
  ],
  "word": "bag of mystery"
}

{
  "etymology_text": "From its construction and possibly dubious ingredients; compare mystery meat.",
  "forms": [
    {
      "form": "bags of mystery",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {
        "1": "bags of mystery"
      },
      "expansion": "bag of mystery (plural bags of mystery)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "related": [
    {
      "word": "mystery bag"
    }
  ],
  "senses": [
    {
      "categories": [
        "English countable nouns",
        "English entries with incorrect language header",
        "English humorous terms",
        "English lemmas",
        "English multiword terms",
        "English nouns",
        "English slang",
        "English terms with obsolete senses",
        "Pages with 1 entry",
        "Pages with entries"
      ],
      "glosses": [
        "A sausage."
      ],
      "links": [
        [
          "humorous",
          "humorous"
        ],
        [
          "sausage",
          "sausage"
        ]
      ],
      "raw_glosses": [
        "(slang, humorous, obsolete) A sausage."
      ],
      "tags": [
        "humorous",
        "obsolete",
        "slang"
      ]
    }
  ],
  "word": "bag of mystery"
}