1. 'I heard her scream twice last night'
2. 'Claire was seen to leave the house before midnight'
I came across these two sentences in close succession in an English test.
When I read the first one, I thought 'scream' was a verb. Seeing how a verb in infinitive 'to leave' is used in a similar structure (or at least what I consider to be a simililar structure), I am now beginning to think that 'scream' in the first sentence was a noun, not a verb.
Is 'scream' a nound in the first sentence?
If not, how to account for the fact that bare infinitive is used in the first sentence while a full infinitive is used in the second?