Well, the book says it eats insects. It eats them three times in it's life and then it's full grown.
5 seconds sound clip from the The Little Shop of Horrors (1960) movie soundboard.
You can hear this line at 00:31:20.837 in the Blu-ray version of the movie.
Quote context
[...]
- 85.
- Now look, Seymour. You gave this plant a fancy name: Audrey Jr.
- But I want to know right now what do just people call it?
- Well, it's a cross between a butterworth and a venus flytrap.
- And what are the habits of this Venus flytrap?
- Well, the book says it eats insects. It eats them three times in it's life and then it's full grown.
- Excellent! And how many times is this one eat?
- Well, this is kind of an unusual type flytrap.
- It may never eat again. I don't see how it could get any bigger.
- Then you think it don't need any more flies?
- Yeah.
[...]