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| Written by | Renee Tawa |
| Illustrator | Bob Berry |
| Published | 2011 |
| Publisher | Publications International |
| Series | Play-a-Sound |
| ISBN | 9781450808927 |
It Must Be a Monster! is a 2011 Sesame Street Play-a-Sound storybook. Abby Cadabby has a sleepover at Elmo's house, and everything seems scary in the dark. Elmo teaches her that when you turn on the light, you can see that there's nothing to be afraid of.
The book has six sound buttons, and a built-in light. Readers can turn on the light switch, and the light will turn on for 15 seconds.