Well, let's see... the chemistry set I had when I was a kid was obvious (and did result in explosions).
But the construx blocks... those were a hazard :-p For the uninitiated, construx were made of two components, a beam and a "joint". The beams snapped over little plastic ears on the joints, and there were other little mechanical dongles and widgets, joints with flat ends, joints that hinged, joints that snapped onto "standard' joints and could spin....
Anyhow, that and a bag of rubber bands culminated in a tube-like "crossbow". And before you snicker at the assembly, within ten minutes of nailing down the "final variant" I'd accidentally shot a "bolt" clear through the ceiling into the attic. It was rapidly disassembled, not by choice :-D
I spent the last youthful years tinkering with those making models of reciprocating assemblies and cars with functioning suspension systems... hrmm. Wonder if I can find a tub of them cheaply these days?
EDIT: Just remembered I've still got the old ones... and if I remember right they're completely ragged out.
