Hover over the different sprites to see whether they detect the mouse or not. Click and drag the sprites to move them.
This project demonstrates that a hidden sprite can detect the mouse, even though it can't detect another sprite. The only way to prevent a sprite from detecting the mouse seems to be using a transparent fill, or an empty costume. A is a normal sprite. B is hidden. C has ghost effect set to 100. D has a transparent fill. Since none of B, C and D are visible, separate sprites are used to show their size and position. All but D detect the mouse. Only C detects A. B detects the mouse, but not A. Thanks to @colinmacc for informing me and inspiring this project with the following comment: https://scratch.mit.edu/studios/25643089/comments/#comments-159959444
