A little birthday fun may be unfairly labeling this lion a bit of a coward... he's a bit startled when the bubble pops!
And that's what makes it fun...
Admit it... this was the first thing you thought of after seeing that!
And just in case the legal people see this post... here's your warning. Do not try this at home. Or the jungle. Or the zoo. After a while, lions may not like being laughed at. Just saying.