PUZZLE 029 A Nonsensical Sentence

Two people are chatting at work while using their computers.
'My ????? is acting strange today.'
'I didnt't know you had a pet!'
The conversation doesn't seem to make sense.
See if you can work out the five-letter word that goes in the place of the '?????'.

Hint 1

The second person thinks the first person is talking about their pet, but that is a misunderstanding.

Hint 2

The confusion has come about because the same word has different meanings.

Hint 3

Something was acting strange while they were using the computer.

Super Hint

What do you use to operate a computer that has the same name as an animal?

Answer for 'A Nonsensical Sentence'

The answer is 'MOUSE'.