An angered enderman slightly increases height, to trigger a tripwire

I had an idea for an "Ender Target" block that detects when you look at it, but this could be accomplished much easier with mechanics that already exist. Make it so that when an enderman is angered by looking at it, the actual height of the entity increases along with the visual height change.

That way, you could put a tripwire above an enderman in a boat that gets activated when the enderman angers, and have a device that can detect a player looking at it.

You could hide the enderman with a painting, and have some kind of secret door where you have to look at a painting to activate it