Here is an old photo of Flash, Tigger and Alex from January 2, 2006. Flash and Tigger lost their mother at a very young age and because of that, I assume, Tigger developed a need to suck on Flash’s belly like he was nursing. Sometimes when Tigger did that Flash would lick himself on the chest at the same time. Here, Alex joined in on the fun.
As they got older, Flash became increasingly irritated with Tigger and eventually put an end to the belly sucking.