Read the following paragraph and answer the question. Give ONLY the answer, no other words or explanation.

For example:

Answer: <most likely answer, as short as possible>.

Paragraph: I heard some cackling in the background ( I hope they were n't watching it on the monitor ) . I tried to do it as quickly as possible . A couple of times , someone tried to open the door .

Question: What is a likely source of the cackling that was heard by the speaker ?
Someone is watching them and laughing
Unknown. The text does not provide enough information to determine the source of the cackling.