Without my first, I am everything. Add an -e and I become a sentient electronic thing. My last two are twins, sure as can be, and to hold your roof, you need at least three of me.

A declaration by a famous sleuth. A type of particle. A school where one probably learned to spell this.

At night my children stab me, That's how I make their bed, Some look out with hollow eyes, The others have large heads, My children have two serpents: One flat, one thin I'm told, One stretches and squeezes to size things up, The other binds and holds.

A tool of three letters, though you can use two, The simplest of levers, And has a wedge, too.

I can be found on the dessert just lounging around with pricky body waiting for you wave back and say Hi.