[Grammar] what he did was

[mmasny]

Which of these are correct grammatically and which are used?
What he did was blow off her head.
What he did was blew off her head.
What he did was blowing off her head.
What he did was to blow off her head.

My guess is that the third one is correct and unused and the first correct and used, but maybe I'm wrong?

 

[Kondorosi]

Which of these are correct grammatically and which are used?
What he did was blow off her head.
What he did was blew off her head.
What he did was blowing off her head.
What he did was to blow off her head.

My guess is that the third one is correct and unused and the first correct and used, but maybe I'm wrong?

It is a pseudo-cleft construction. Use the bare infinitive structure:

What he did was blow off her head.

 

[2006]

What he did was blow her head off.

 

[Ramanu]

Which of these are correct grammatically and which are used?
What he did was blow off her head.
What he did was blew off her head.
What he did was blowing off her head.
What he did was to blow off her head.

My guess is that the third one is correct and unused and the first correct and used, but maybe I'm wrong?

My guess is that the fourth one is correct and unused, but maybe I'm wrong?