Always looks rather gruesome to me.
Apr 28, Cherry trees are best pruned in mid summer to avoid a specific fungal disease called silver leaf.
This can cause the death of branches. The spores of silver leaf are active from September to May so to avoid them getting into the tree its best to do any pruning as mentioned above.
That is the sap from the cherry tree.
Cacoethes: An irresistible urge to do something inadvisable. Feb 10, How to prune old, existing, mature cherry treesMusic:"Modern Jazz Samba" Kevin MacLeod (bushnotch.bar).