arduino as i2c slave?

Hi,
Can an arduino be used as an i2c device? a slave?
If so, can it be used as IO expanders or something like another cpu?
I googled it but none of the websites and documentation are easy enough for me to understand.

Thanks!

Look at the I2C / wire examples in the reference section. The master/slave examples show communication between two arduinos over I2C

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