With my Cheshire cat blank there are two main ways you can attach the elastic. The first is by gluing it in, which is what I recommend if you dont like power tools. The second is drill holes for elastic.

On my Cheshire cat blank there are suggested divots on the sides of the mask for where you can drill out and put in elastic. However, I put the divot a little too high on the cheek and the holes are too close to the outside of the mask. While the resin is strong, I am unsure how long term strain with elastic would hold on this area, and if you drill at the divot point i suggest reenforcing the area.

This is a solution if you do not want to re enforce, and still want the holes for elastic. On the picture there is labeled "divot". This is the indent where it is implied you should drill for elastic holes. If you make a mark 1/4" inward from the divot and drill with that mark as the center you get a hole that has at least 1cm of resin between it and the outside, making it more resilient to strain and does not need to be reenforced. If you are worried about the divot still being there, it can easily be filled with a dot of plumbers apoxy, or taxidermist apoxy, which while it does not look pretty initially- can be sanded and painted over easily.

If I re make this mold some day I will fix this issue, but for now I am just happy there is a simple solution of moving the hole slightly inward.