OK lets assume this is a one off after a long week and it is not you DH's usual behaviour.
This HAS to be a one off.
There are two adults and a 3 year old in the house. Three year olds take things to look at and then leave them in unexpected places, they post letters through a gap in floorboards, out the post box and down the toilet. Be thankful we all have streaming / digital TV because they used to put things in VHS recorders, toast was a favorite.
That's what 3 year olds do.
This is why adults put things out of reach.
One of an adult's many jobs (not just parents) is to model good behavior and appropriate responses.
A Parent, should among other things, provide a place of safety for their child.
This was keys, it could have been alcohol or medication, or a glass ornament, or 1000 other things a child might want to look at but an adult has a duty to keep them away from.
Yes please do tell your DH to read this. Parenting is a fucking hard job, it's one of the reasons I never had children.
Life can be tiring, difficult, draining but none of that is the fault of a 3 year old.