Can a witness be compelled to do more than show that the answer to the question is likely to be dangerous to him?

Obviously a witness may not be compelled to do more than show that the answer is likely to be dangerous to him, else he will be forced to disclose those very facts which the privilege protects. Logically, indeed, he is boxed in a paradox, for he must prove the criminatory character of what it is his privilege to suppress just because it is criminatory. The only practicable solution is to be content with the door's being set a little ajar, and while at times this no doubt partially destroys the privilege, and at times it permits the suppression of competent evidence, nothing better is available.

United States v. Weisman, supra, 111 F.2d at 262.