If an XOR has identical inputs the output will be always 0,
If there is a transient delay of one input relative to the other, then the output =1 for the duration of the delay. If the delay is uniform for rising or falling edge, then there will be 1 pulse for each input transition pair rising and falling , thus 2 pulses per cycle of input.
A simple fixed circuit uses an inverter gate on one input leg so the output is always =1 except during the input transition then it pulses low.
Using an XNOR gives the opposite output polarity.