Recall didn't work

Suki's recall is normally spot on. I trained her for weeks using steak as a reward and would practice for hours each day. Normally people are amazed as I can simply say Suki to me and she comes sprinting. I stole the to me from the Dark Tower by Stephen King    Suki also loves people but there is this one guy at the park that she barks fiercely at every time he gets in the area. The other day Suki was off lead and saw him coming before I did. She started running off and barking before I could catch her. I tried the to me but no luck which gave everyone a good laugh. Suki just barks and barks at hiim but is still wagging her tail. I can't figure out why though

How strange!

Very strange I have no idea why she does it but every time she sees him she barks. Although she lets him pet her without an issue