OR, 'That animal we spotted on the safari was spotted on the skin'. That animal we saw on the safari had spots on it's skin.

If you say "I spotted him on the train", it means the same as "I saw (to see) him on the train"

often used to "denote" an important person was seen somewhere: ex: Madona was spotted at the Soho Gallery in London. You did not have a big chance to look at her or be seen yourself, "Madona" was probably walking by and you got a glimpse of her as she passed by an open doorway and you just happened to SPOT her. or as in the first part of Derrick's example you were looking at animals while on safary and you spotted an animal that had spots on its skin. Could have been stripes (different animal).