"Ostrovsky came [to the party], and what a great man he is, frighteningly intelligent, but also very warm, quite unlike this Ermil", he continued a month later.

Everything I've seen about you tells me you're frighteningly intelligent, and I think your teachers are in for a challenge if they want to keep up with you.

His eyes popped open bright, electric, frighteningly intelligent.

This being, this representative of a mature species, was frighteningly intelligent in obscure ways.

He was young, still in his late teens by human standards, but frighteningly intelligent and already useful to have around engineering when they were short handed.

Yet the heavy-boned dark face was too alive and aware to be an animal's, and the dark eyes were searching, restless, almost frighteningly intelligent.

On the other hand, he is frighteningly intelligent.

The big one looks frighteningly intelligent, if you ask me, and the little one is a flirt.

These folk were frighteningly intelligent and cynical.

Here's the problem there: several of the members have shown themselves to be frighteningly intelligent when it comes to hacking and covering tracks.