my $fo = q{}; # fo variable is initialized

# ... run code, run... 
# (fo will be updated with a real value in this part)
# ... but something forrible happens instead...

print "My homework: $fo"      ; # prints "My homework: " and exits 

print 'My homework: ',($fo || 'Roses are red, violets are blue. Fo was still empty, so I improvised a default value'); # with poetic results

print 'we have ', ($fo + 2 || 8), 'beans'; # prints: we have 2 beans
print 'we have ', ($fo + 0), 'beans';      # prints: we have 0 beans
print 'we have ',($fo + 0 || 8),'beans';   # but here prints: we have 8 beans, Why?