Water-sensetive recyling bin closer

In some localities, householders are provided with "wheelie bins" for garden waste.

These bins have a hinged lid.

If a bin is filled with fresh cut grass, and the lid is left propped open with a stick, on a sunny day* the bin heats up and much moisture evaporates, causing the contents to shrink and allowing more material to be loaded.

But if it rains**, the rain wets the cuttings and accumulates in the bin. Not good.

BorgCo engineers have developd an automatic bin-closer to prevent this problem. The device consists of a wooden lath, at the end of which is a mechanism resembling a mousetrap. This is prevented from operating by a soluble aspirin tablet, above which is a small funnel.

When it rains, water is collected by the funnel and dripped onto the aspirin, which dissolves. The spring is released and the arm flips the lath clear of the bin, allowing the lid to fall shut under the influence of gravity***

*Readers in the UK may not be familiar with this.
**Readers in the UK will definitely be familiar with this.
***Gravity not included.